c99_alloca.h: Include stdlib.h on all non-Windows.

Fix build on FreeBSD.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89364
Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Tested-by: Brian Paul <brianp@vmware.com>
diff --git a/include/c99_alloca.h b/include/c99_alloca.h
index 7a81c50..575f719 100644
--- a/include/c99_alloca.h
+++ b/include/c99_alloca.h
@@ -35,13 +35,9 @@
 
 #  define alloca _alloca
 
-#elif defined(__MINGW32__)
-
-#  include <malloc.h>
-
 #else /* !defined(_MSC_VER) */
 
-#  include <alloca.h>
+#  include <stdlib.h>
 
 #endif /* !defined(_MSC_VER) */