app-text/texlive-core-2019-r4 fails to compile with LTO
while configuring libs/cairo:

checking whether float word ordering is bigendian... unknown
configure: error: 

Unknown float word ordering. You need to manually preset
ax_cv_c_float_words_bigendian=no (or yes) according to your system.

In cairo the issue has been fixed long ago in commit 7cfebce.
In the texlive source the fixed autoconf macro is available
as libs/cairo/cairo-src/build/aclocal.float.m4, but the one
actually used (libs/cairo/m4/float.m4) is still broken.
Replace the broken file with the fixed copy.

Bug: https://bugs.gentoo.org/688544

--- texlive-20190410-source/libs/cairo/m4/float.m4.orig
+++ texlive-20190410-source/libs/cairo/m4/float.m4
@@ -12,7 +12,7 @@ AC_DEFUN([AX_C_FLOAT_WORDS_BIGENDIAN],
   [AC_CACHE_CHECK(whether float word ordering is bigendian,
                   ax_cv_c_float_words_bigendian, [
 
-# The endianess is detected by first compiling C code that contains a special
+# The endianness is detected by first compiling C code that contains a special
 # double float value, then grepping the resulting object file for certain
 # strings of ascii values. The double is specially crafted to have a
 # binary representation that corresponds with a simple string. In this
@@ -24,16 +24,17 @@ AC_DEFUN([AX_C_FLOAT_WORDS_BIGENDIAN],
 # is found, the user is instructed to specify the ordering.
 
 ax_cv_c_float_words_bigendian=unknown
-AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
+AC_LINK_IFELSE([AC_LANG_SOURCE([[
 
-double d = 90904234967036810337470478905505011476211692735615632014797120844053488865816695273723469097858056257517020191247487429516932130503560650002327564517570778480236724525140520121371739201496540132640109977779420565776568942592.0;
+double d __attribute__((used)) = 90904234967036810337470478905505011476211692735615632014797120844053488865816695273723469097858056257517020191247487429516932130503560650002327564517570778480236724525140520121371739201496540132640109977779420565776568942592.0;
+int main() { return 0; }
 
 ]])], [
 
-if strings - conftest.$ac_objext | grep noonsees >/dev/null ; then
+if strings -a conftest$ac_exeext | grep noonsees >/dev/null ; then
   ax_cv_c_float_words_bigendian=yes
 fi
-if strings - conftest.$ac_objext | grep seesnoon >/dev/null ; then
+if strings -a conftest$ac_exeext | grep seesnoon >/dev/null ; then
   if test "$ax_cv_c_float_words_bigendian" = unknown; then
     ax_cv_c_float_words_bigendian=no
   else
--- texlive-20190410-source/libs/cairo/configure.orig
+++ texlive-20190410-source/libs/cairo/configure
@@ -5650,7 +5650,7 @@ if ${ax_cv_c_float_words_bigendian+:} fa
 else
 
 
-# The endianess is detected by first compiling C code that contains a special
+# The endianness is detected by first compiling C code that contains a special
 # double float value, then grepping the resulting object file for certain
 # strings of ascii values. The double is specially crafted to have a
 # binary representation that corresponds with a simple string. In this
@@ -5666,17 +5666,18 @@ cat confdefs.h - <<_ACEOF >conftest.$ac_
 /* end confdefs.h.  */
 
 
-double d = 90904234967036810337470478905505011476211692735615632014797120844053488865816695273723469097858056257517020191247487429516932130503560650002327564517570778480236724525140520121371739201496540132640109977779420565776568942592.0;
+double d __attribute__((used)) = 90904234967036810337470478905505011476211692735615632014797120844053488865816695273723469097858056257517020191247487429516932130503560650002327564517570778480236724525140520121371739201496540132640109977779420565776568942592.0;
+int main() { return 0; }
 
 
 _ACEOF
-if ac_fn_c_try_compile "$LINENO"; then :
+if ac_fn_c_try_link "$LINENO"; then :
 
 
-if strings - conftest.$ac_objext | grep noonsees >/dev/null ; then
+if strings -a conftest$ac_exeext | grep noonsees >/dev/null ; then
   ax_cv_c_float_words_bigendian=yes
 fi
-if strings - conftest.$ac_objext | grep seesnoon >/dev/null ; then
+if strings -a conftest$ac_exeext | grep seesnoon >/dev/null ; then
   if test "$ax_cv_c_float_words_bigendian" = unknown; then
     ax_cv_c_float_words_bigendian=no
   else
@@ -5686,7 +5687,8 @@ fi
 
 
 fi
-rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext conftest.$ac_ext
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ax_cv_c_float_words_bigendian" >&5
 $as_echo "$ax_cv_c_float_words_bigendian" >&6; }