https://bugs.gentoo.org/900310
https://github.com/rdesktop/rdesktop/pull/407

From 0a38f855c2f6bb197539fbb9ec0ce5a97775a178 Mon Sep 17 00:00:00 2001
From: Florian Weimer <fweimer@redhat.com>
Date: Tue, 18 Apr 2023 09:55:39 +0200
Subject: [PATCH] configure.ac: Fix statvfs64 check for C99 compatibility

C99 does not support implicit ints and implicit function declarations
(such as exit here).  Avoid them, so that the configure check does
not fail unconditionally with such compilers.
--- a/configure.ac
+++ b/configure.ac
@@ -668,12 +668,13 @@ if test $space = no; then
   # SVR4
   AC_CACHE_CHECK([statvfs64 function (SVR4)], fu_cv_sys_stat_statvfs64,
   [AC_TRY_RUN([
+#include <stdlib.h>
 #if defined(HAVE_UNISTD_H)
 #include <unistd.h>
 #endif
 #include <sys/types.h>
 #include <sys/statvfs.h>
-  main ()
+  int main (void)
   {
     struct statvfs64 fsd;
     exit (statvfs64 (".", &fsd));