See https://bugs.gentoo.org/show_bug.cgi?id=577238

diff -Naur gcc-4.8.5.orig/libstdc++-v3/config/locale/generic/c_locale.h gcc-4.8.5/libstdc++-v3/config/locale/generic/c_locale.h
--- gcc-4.8.5.orig/libstdc++-v3/config/locale/generic/c_locale.h	2013-02-03 17:54:05.000000000 +0000
+++ gcc-4.8.5/libstdc++-v3/config/locale/generic/c_locale.h	2016-03-12 22:33:21.704000000 +0000
@@ -70,7 +70,7 @@
     __builtin_va_list __args;
     __builtin_va_start(__args, __fmt);
 
-#ifdef _GLIBCXX_USE_C99
+#if defined(_GLIBCXX_USE_C99) || defined(__UCLIBC__)
     const int __ret = __builtin_vsnprintf(__out, __size, __fmt, __args);
 #else
     const int __ret = __builtin_vsprintf(__out, __fmt, __args);
diff -Naur gcc-4.8.5.orig/libstdc++-v3/config/locale/gnu/c_locale.h gcc-4.8.5/libstdc++-v3/config/locale/gnu/c_locale.h
--- gcc-4.8.5.orig/libstdc++-v3/config/locale/gnu/c_locale.h	2013-02-03 17:54:05.000000000 +0000
+++ gcc-4.8.5/libstdc++-v3/config/locale/gnu/c_locale.h	2016-03-12 22:33:21.704000000 +0000
@@ -88,7 +88,7 @@
     __builtin_va_list __args;
     __builtin_va_start(__args, __fmt);
 
-#ifdef _GLIBCXX_USE_C99
+#if defined(_GLIBCXX_USE_C99) || defined(__UCLIBC__)
     const int __ret = __builtin_vsnprintf(__out, __size, __fmt, __args);
 #else
     const int __ret = __builtin_vsprintf(__out, __fmt, __args);
diff -Naur gcc-4.8.5.orig/libstdc++-v3/include/bits/basic_string.h gcc-4.8.5/libstdc++-v3/include/bits/basic_string.h
--- gcc-4.8.5.orig/libstdc++-v3/include/bits/basic_string.h	2013-05-15 22:00:48.000000000 +0000
+++ gcc-4.8.5/libstdc++-v3/include/bits/basic_string.h	2016-03-12 22:35:30.648000000 +0000
@@ -2809,7 +2809,7 @@
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace
 
-#if ((__cplusplus >= 201103L) && defined(_GLIBCXX_USE_C99) \
+#if ((__cplusplus >= 201103L) && (defined(_GLIBCXX_USE_C99) || defined(__UCLIBC__)) \
      && !defined(_GLIBCXX_HAVE_BROKEN_VSWPRINTF))
 
 #include <ext/string_conversions.h>
diff -Naur gcc-4.8.5.orig/libstdc++-v3/include/bits/basic_string.h.rej gcc-4.8.5/libstdc++-v3/include/bits/basic_string.h.rej
--- gcc-4.8.5.orig/libstdc++-v3/include/bits/basic_string.h.rej	1970-01-01 00:00:00.000000000 +0000
+++ gcc-4.8.5/libstdc++-v3/include/bits/basic_string.h.rej	2016-03-12 22:33:21.704000000 +0000
@@ -0,0 +1,11 @@
+--- libstdc++-v3/include/bits/basic_string.h	2015-05-28 16:27:46.000000000 +0000
++++ libstdc++-v3/include/bits/basic_string.h	2016-03-12 19:21:06.416000000 +0000
+@@ -2844,7 +2844,7 @@
+ _GLIBCXX_END_NAMESPACE_VERSION
+ } // namespace
+ 
+-#if __cplusplus >= 201103L && defined(_GLIBCXX_USE_C99)
++#if __cplusplus >= 201103L && (defined(_GLIBCXX_USE_C99) || defined(__UCLIBC__))
+ 
+ #include <ext/string_conversions.h>
+ 
diff -Naur gcc-4.8.5.orig/libstdc++-v3/include/bits/locale_facets.tcc gcc-4.8.5/libstdc++-v3/include/bits/locale_facets.tcc
--- gcc-4.8.5.orig/libstdc++-v3/include/bits/locale_facets.tcc	2013-02-03 17:54:05.000000000 +0000
+++ gcc-4.8.5/libstdc++-v3/include/bits/locale_facets.tcc	2016-03-12 22:33:21.704000000 +0000
@@ -987,7 +987,7 @@
 	char __fbuf[16];
 	__num_base::_S_format_float(__io, __fbuf, __mod);
 
-#ifdef _GLIBCXX_USE_C99
+#if defined(_GLIBCXX_USE_C99) || defined(__UCLIBC__)
 	// First try a buffer perhaps big enough (most probably sufficient
 	// for non-ios_base::fixed outputs)
 	int __cs_size = __max_digits * 3;
diff -Naur gcc-4.8.5.orig/libstdc++-v3/include/bits/locale_facets_nonio.tcc gcc-4.8.5/libstdc++-v3/include/bits/locale_facets_nonio.tcc
--- gcc-4.8.5.orig/libstdc++-v3/include/bits/locale_facets_nonio.tcc	2013-02-03 17:54:05.000000000 +0000
+++ gcc-4.8.5/libstdc++-v3/include/bits/locale_facets_nonio.tcc	2016-03-12 22:33:21.708000000 +0000
@@ -572,7 +572,7 @@
     {
       const locale __loc = __io.getloc();
       const ctype<_CharT>& __ctype = use_facet<ctype<_CharT> >(__loc);
-#ifdef _GLIBCXX_USE_C99
+#if defined(_GLIBCXX_USE_C99) || defined(__UCLIBC__)
       // First try a buffer perhaps big enough.
       int __cs_size = 64;
       char* __cs = static_cast<char*>(__builtin_alloca(__cs_size));
@@ -745,7 +745,7 @@
 		case 'S':
 		  // Seconds. [tm_sec]
 		  // [00, 60] in C99 (one leap-second), [00, 61] in C89.
-#ifdef _GLIBCXX_USE_C99
+#if defined(_GLIBCXX_USE_C99) || defined(__UCLIBC__)
 		  __beg = _M_extract_num(__beg, __end, __tm->tm_sec, 0, 60, 2,
 #else
 		  __beg = _M_extract_num(__beg, __end, __tm->tm_sec, 0, 61, 2,
diff -Naur gcc-4.8.5.orig/libstdc++-v3/include/c_compatibility/math.h gcc-4.8.5/libstdc++-v3/include/c_compatibility/math.h
--- gcc-4.8.5.orig/libstdc++-v3/include/c_compatibility/math.h	2013-02-03 17:54:05.000000000 +0000
+++ gcc-4.8.5/libstdc++-v3/include/c_compatibility/math.h	2016-03-12 22:33:21.708000000 +0000
@@ -56,7 +56,7 @@
 using std::floor;
 using std::fmod;
 
-#if _GLIBCXX_USE_C99
+#if defined(_GLIBCXX_USE_C99) || defined(__UCLIBC__)
 using std::fpclassify;
 using std::isfinite;
 using std::isinf;
diff -Naur gcc-4.8.5.orig/libstdc++-v3/include/c_compatibility/wchar.h gcc-4.8.5/libstdc++-v3/include/c_compatibility/wchar.h
--- gcc-4.8.5.orig/libstdc++-v3/include/c_compatibility/wchar.h	2013-02-03 17:54:05.000000000 +0000
+++ gcc-4.8.5/libstdc++-v3/include/c_compatibility/wchar.h	2016-03-12 22:33:21.708000000 +0000
@@ -103,7 +103,7 @@
 using std::wmemset;
 using std::wcsftime;
 
-#if _GLIBCXX_USE_C99
+#if defined(_GLIBCXX_USE_C99) || defined(__UCLIBC__)
 using std::wcstold;
 using std::wcstoll;
 using std::wcstoull;
diff -Naur gcc-4.8.5.orig/libstdc++-v3/include/c_global/cstdio gcc-4.8.5/libstdc++-v3/include/c_global/cstdio
--- gcc-4.8.5.orig/libstdc++-v3/include/c_global/cstdio	2016-03-12 22:30:28.980000000 +0000
+++ gcc-4.8.5/libstdc++-v3/include/c_global/cstdio	2016-03-12 22:33:21.708000000 +0000
@@ -139,7 +139,7 @@
   using ::vsprintf;
 } // namespace
 
-#if _GLIBCXX_USE_C99
+#if defined(_GLIBCXX_USE_C99) || defined(__UCLIBC__)
 
 #undef snprintf
 #undef vfscanf
diff -Naur gcc-4.8.5.orig/libstdc++-v3/include/c_global/cstdlib gcc-4.8.5/libstdc++-v3/include/c_global/cstdlib
--- gcc-4.8.5.orig/libstdc++-v3/include/c_global/cstdlib	2013-02-11 23:42:43.000000000 +0000
+++ gcc-4.8.5/libstdc++-v3/include/c_global/cstdlib	2016-03-12 22:33:21.708000000 +0000
@@ -182,7 +182,7 @@
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace
 
-#if _GLIBCXX_USE_C99
+#if defined(_GLIBCXX_USE_C99) || defined(__UCLIBC__)
 
 #undef _Exit
 #undef llabs
diff -Naur gcc-4.8.5.orig/libstdc++-v3/include/c_global/cwchar gcc-4.8.5/libstdc++-v3/include/c_global/cwchar
--- gcc-4.8.5.orig/libstdc++-v3/include/c_global/cwchar	2013-02-03 17:54:05.000000000 +0000
+++ gcc-4.8.5/libstdc++-v3/include/c_global/cwchar	2016-03-12 22:33:21.708000000 +0000
@@ -232,7 +232,7 @@
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace
 
-#if _GLIBCXX_USE_C99
+#if defined(_GLIBCXX_USE_C99) || defined(__UCLIBC__)
 
 #undef wcstold
 #undef wcstoll
@@ -289,7 +289,7 @@
   using std::vwscanf;
 #endif
 
-#if _GLIBCXX_USE_C99
+#if defined(_GLIBCXX_USE_C99) || defined(__UCLIBC__)
   using std::wcstold;
   using std::wcstoll;
   using std::wcstoull;
diff -Naur gcc-4.8.5.orig/libstdc++-v3/include/c_std/cstdio gcc-4.8.5/libstdc++-v3/include/c_std/cstdio
--- gcc-4.8.5.orig/libstdc++-v3/include/c_std/cstdio	2013-02-03 17:54:05.000000000 +0000
+++ gcc-4.8.5/libstdc++-v3/include/c_std/cstdio	2016-03-12 22:33:21.712000000 +0000
@@ -139,7 +139,7 @@
   using ::vsprintf;
 } // namespace std
 
-#if _GLIBCXX_USE_C99
+#if defined(_GLIBCXX_USE_C99) || defined(__UCLIBC__)
 
 #undef snprintf
 #undef vfscanf
diff -Naur gcc-4.8.5.orig/libstdc++-v3/include/c_std/cstdlib gcc-4.8.5/libstdc++-v3/include/c_std/cstdlib
--- gcc-4.8.5.orig/libstdc++-v3/include/c_std/cstdlib	2013-02-12 12:01:14.000000000 +0000
+++ gcc-4.8.5/libstdc++-v3/include/c_std/cstdlib	2016-03-12 22:33:21.712000000 +0000
@@ -180,7 +180,7 @@
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace
 
-#if _GLIBCXX_USE_C99
+#if defined(_GLIBCXX_USE_C99) || defined(__UCLIBC__)
 
 #undef _Exit
 #undef llabs
diff -Naur gcc-4.8.5.orig/libstdc++-v3/include/c_std/cwchar gcc-4.8.5/libstdc++-v3/include/c_std/cwchar
--- gcc-4.8.5.orig/libstdc++-v3/include/c_std/cwchar	2013-02-03 17:54:05.000000000 +0000
+++ gcc-4.8.5/libstdc++-v3/include/c_std/cwchar	2016-03-12 22:33:21.712000000 +0000
@@ -228,7 +228,7 @@
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace
 
-#if _GLIBCXX_USE_C99
+#if defined(_GLIBCXX_USE_C99) || defined(__UCLIBC__)
 
 #undef wcstold
 #undef wcstoll
diff -Naur gcc-4.8.5.orig/libstdc++-v3/include/ext/vstring.h gcc-4.8.5/libstdc++-v3/include/ext/vstring.h
--- gcc-4.8.5.orig/libstdc++-v3/include/ext/vstring.h	2013-02-03 17:54:05.000000000 +0000
+++ gcc-4.8.5/libstdc++-v3/include/ext/vstring.h	2016-03-12 22:33:21.712000000 +0000
@@ -2571,7 +2571,7 @@
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace
 
-#if ((__cplusplus >= 201103L) && defined(_GLIBCXX_USE_C99))
+#if ((__cplusplus >= 201103L) && (defined(_GLIBCXX_USE_C99) || definied(__UCLIBC__)))
 
 #include <ext/string_conversions.h>
 
diff -Naur gcc-4.8.5.orig/libstdc++-v3/include/tr1/cstdio gcc-4.8.5/libstdc++-v3/include/tr1/cstdio
--- gcc-4.8.5.orig/libstdc++-v3/include/tr1/cstdio	2013-02-03 17:54:05.000000000 +0000
+++ gcc-4.8.5/libstdc++-v3/include/tr1/cstdio	2016-03-12 22:33:21.712000000 +0000
@@ -33,7 +33,7 @@
 
 #include <cstdio>
 
-#if _GLIBCXX_USE_C99
+#if defined(_GLIBCXX_USE_C99) || defined(__UCLIBC__)
 
 namespace std _GLIBCXX_VISIBILITY(default)
 {
diff -Naur gcc-4.8.5.orig/libstdc++-v3/include/tr1/cstdlib gcc-4.8.5/libstdc++-v3/include/tr1/cstdlib
--- gcc-4.8.5.orig/libstdc++-v3/include/tr1/cstdlib	2013-02-03 17:54:05.000000000 +0000
+++ gcc-4.8.5/libstdc++-v3/include/tr1/cstdlib	2016-03-12 22:33:21.712000000 +0000
@@ -35,7 +35,7 @@
 
 #if _GLIBCXX_HOSTED
 
-#if _GLIBCXX_USE_C99
+#if defined(_GLIBCXX_USE_C99) || defined(__UCLIBC__)
 
 namespace std _GLIBCXX_VISIBILITY(default)
 {
diff -Naur gcc-4.8.5.orig/libstdc++-v3/include/tr1/cwchar gcc-4.8.5/libstdc++-v3/include/tr1/cwchar
--- gcc-4.8.5.orig/libstdc++-v3/include/tr1/cwchar	2013-02-03 17:54:05.000000000 +0000
+++ gcc-4.8.5/libstdc++-v3/include/tr1/cwchar	2016-03-12 22:33:21.712000000 +0000
@@ -52,7 +52,7 @@
   using std::vwscanf;
 #endif
 
-#if _GLIBCXX_USE_C99
+#if defined(_GLIBCXX_USE_C99) || defined(__UCLIBC__)
   using std::wcstold;
   using std::wcstoll;
   using std::wcstoull;
diff -Naur gcc-4.8.5.orig/libstdc++-v3/include/tr1/stdlib.h gcc-4.8.5/libstdc++-v3/include/tr1/stdlib.h
--- gcc-4.8.5.orig/libstdc++-v3/include/tr1/stdlib.h	2013-02-03 17:54:05.000000000 +0000
+++ gcc-4.8.5/libstdc++-v3/include/tr1/stdlib.h	2016-03-12 22:33:21.716000000 +0000
@@ -33,7 +33,7 @@
 
 #if _GLIBCXX_HOSTED
 
-#if _GLIBCXX_USE_C99
+#if defined(_GLIBCXX_USE_C99) || defined(__UCLIBC__)
 
 using std::tr1::atoll;
 using std::tr1::strtoll;
diff -Naur gcc-4.8.5.orig/libstdc++-v3/src/c++11/debug.cc gcc-4.8.5/libstdc++-v3/src/c++11/debug.cc
--- gcc-4.8.5.orig/libstdc++-v3/src/c++11/debug.cc	2013-02-03 17:54:05.000000000 +0000
+++ gcc-4.8.5/libstdc++-v3/src/c++11/debug.cc	2016-03-12 22:33:21.716000000 +0000
@@ -787,7 +787,7 @@
 				     int __n __attribute__ ((__unused__)), 
 				     const char* __fmt, _Tp __s) const throw ()
     {
-#ifdef _GLIBCXX_USE_C99
+#if defined(_GLIBCXX_USE_C99) || defined(__UCLIBC__)
       std::snprintf(__buf, __n, __fmt, __s);
 #else
       std::sprintf(__buf, __fmt, __s);