--- /dev/null	2016-06-21 17:16:19.999912614 +0200
+++ seamonkey-2.40/mozilla/build/autoconf/need-latomic.m4	2016-06-21 21:09:21.469043320 +0200
@@ -0,0 +1,28 @@
+AC_DEFUN([MOZ_NEED_LATOMIC_CHECK],
+[
+  AC_LANG_CPLUSPLUS
+
+  AC_CACHE_CHECK([whether -latomic is needed for proper std::atomic<T> support],
+    [moz_cv_need_latomic],
+
+    [AC_TRY_LINK(
+      [#include <atomic>],
+      [std::atomic<double> at_dbl;
+       at_dbl.store (0.0);],
+
+      [moz_cv_need_latomic=no],
+
+      [_SAVE_LIBS="$LIBS"
+       LIBS="$LIBS -latomic"
+
+       AC_TRY_LINK(
+         [#include <atomic>],
+         [std::atomic<double> at_dbl;
+          at_dbl.store (0.0);],
+
+         [moz_cv_need_latomic=yes],
+         [AC_MSG_WARN([failed to build the test both with and without -latomic])
+          moz_cv_need_latomic=no
+          LIBS="$_SAVE_LIBS"]])
+    ]))
+])
--- seamonkey-2.40.old/mozilla/aclocal.m4	2016-06-21 19:37:08.554498317 +0200
+++ seamonkey-2.40/mozilla/aclocal.m4	2016-06-21 19:45:45.661105009 +0200
@@ -18,6 +18,7 @@
 builtin(include, build/autoconf/mozprog.m4)dnl
 builtin(include, build/autoconf/mozheader.m4)dnl
 builtin(include, build/autoconf/mozcommonheader.m4)dnl
+builtin(include, build/autoconf/need-latomic.m4)dnl
 builtin(include, build/autoconf/lto.m4)dnl
 builtin(include, build/autoconf/frameptr.m4)dnl
 builtin(include, build/autoconf/compiler-opts.m4)dnl
--- seamonkey-2.40.old/mozilla/configure.in	2016-06-21 19:37:57.703082637 +0200
+++ seamonkey-2.40/mozilla/configure.in	2016-06-21 19:46:19.971807400 +0200
@@ -2576,6 +2576,7 @@
 AC_LANG_CPLUSPLUS
 
 MOZ_CXX11
+MOZ_NEED_LATOMIC_CHECK
 
 AC_LANG_C