https://bugs.gentoo.org/879663
https://gitlab.inria.fr/gf2x/gf2x/-/commit/a2f0fd388c12ca0b9f4525c6cfbc515418dcbaf8

From a2f0fd388c12ca0b9f4525c6cfbc515418dcbaf8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Emmanuel=20Thom=C3=A9?= <Emmanuel.Thome@inria.fr>
Date: Thu, 17 Sep 2020 23:40:54 +0200
Subject: [PATCH] fix #include in configure test

See there: https://trac.sagemath.org/ticket/30494
--- a/config/acinclude.m4
+++ b/config/acinclude.m4
@@ -661,6 +661,7 @@ AC_DEFUN([GF2X_PROG_CC_FOR_BUILD_WORKS],
 # remove anything that might look like compiler output to our "||" expression
 rm -f conftest* a.out b.out a.exe a_out.exe
 cat >conftest.c <<EOF
+#include <stdlib.h>
 int
 main ()
 {
@@ -699,6 +700,7 @@ AC_DEFUN([GF2X_PROG_EXEEXT_FOR_BUILD],
 AC_CACHE_CHECK([for build system executable suffix],
                gf2x_cv_prog_exeext_for_build,
 [cat >conftest.c <<EOF
+#include <stdlib.h>
 int
 main ()
 {
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