diff -r 000000000000 -r 6474c204b198 build/autoconf/hotfixes.m4
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/build/autoconf/hotfixes.m4	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,24 @@
+dnl This Source Code Form is subject to the terms of the Mozilla Public
+dnl dnl License, v. 2.0. If a copy of the MPL was not distributed with this
+dnl dnl file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+dnl Set of hotfixes to address issues in autoconf 2.13
+
+dnl Divert AC_CHECK_FUNC so that the #includes it uses can't interfere
+dnl with the function it tests.
+dnl So, when testing e.g. posix_memalign, any #include that AC_CHECK_FUNC
+dnl prints is replaced with:
+dnl   #define posix_memalign innocuous_posix_memalign
+dnl   #include "theinclude"
+dnl   #undef posix_memalign
+dnl This avoids double declaration of that function when the header normally
+dnl declares it, while the test itself is just expecting the function not to be
+dnl declared at all, and declares it differently (which doesn't matter for the
+dnl test itself).
+dnl More recent versions of autoconf are essentially doing this.
+define([ac_cv_func_], [ac_cv_func2_])dnl
+define([_AC_CHECK_FUNC],defn([AC_CHECK_FUNC]))dnl
+define([AC_CHECK_FUNC], [dnl
+patsubst(_AC_CHECK_FUNC($@), [#include.*$], [#define $1 innocuous_$1
+\&
+#undef $1])])dnl