cygwin: disable -Wframe-address warning only on GCC 6 or later

This is required as long as we don't have a GCC 6.x cross compiler
on Linux.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/crt0.c

@@ -20,9 +20,13 @@ void
 mainCRTStartup ()
 {
 #ifdef __i386__
+#if __GNUC_PREREQ(6,0)
 #pragma GCC diagnostic ignored "-Wframe-address"
+#endif
   (void)__builtin_return_address(1);
+#if __GNUC_PREREQ(6,0)
 #pragma GCC diagnostic pop
+#endif
   asm volatile ("andl $-16,%%esp" ::: "%esp");
 #endif
 

winsup/cygwin/init.cc

@@ -22,10 +22,14 @@ static bool dll_finished_loading;
 static void WINAPI
 threadfunc_fe (VOID *arg)
 {
-#ifndef __x86_64__
+#ifdef __i386__
+#if __GNUC_PREREQ(6,0)
 #pragma GCC diagnostic ignored "-Wframe-address"
+#endif
   (void)__builtin_return_address(1);
+#if __GNUC_PREREQ(6,0)
 #pragma GCC diagnostic pop
+#endif
   asm volatile ("andl $-16,%%esp" ::: "%esp");
 #endif
   _cygtls::call ((DWORD (*)  (void *, void *)) TlsGetValue (_my_oldfunc), arg);