diff -r 000000000000 -r 6474c204b198 build/autoconf/lto.m4
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/build/autoconf/lto.m4	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,19 @@
+dnl This Source Code Form is subject to the terms of the Mozilla Public
+dnl License, v. 2.0. If a copy of the MPL was not distributed with this
+dnl file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+dnl check if the build is using lto. This is really primitive and only detects llvm based
+dnl compilers right now.
+AC_DEFUN([MOZ_DOING_LTO],
+[
+  cat > conftest.c <<EOF
+                  int foo = 1;
+EOF
+  $1=no
+  if ${CC-cc} ${CFLAGS} -S conftest.c -o conftest.s >/dev/null 2>&1; then
+    if grep '^target triple =' conftest.s; then
+      $1=yes
+    fi
+  fi
+  rm -f conftest.[cs]
+])