https://bugs.gentoo.org/885311
https://bugs.gentoo.org/899806
--- a/m4/sane.m4
+++ b/m4/sane.m4
@@ -44,6 +44,7 @@ dnl
       AC_TRY_RUN([
 #include <sane/sane.h>
 #include <stdio.h>
+#include <stdlib.h>
 
 int 
 main ()