[Darwin, testsuite, committed] Fix Wnonnull on Darwin.

[Iain Sandoe]

This test has failed always on Darwin, because Darwin does not mark
entries in string.h with nonnull attributes.  Since the purpose of the test
is to check that the warnings are issued for an inlined function, not that
the target headers are marked up, we can provide locally marked up
function declarations for Darwin.

tested on x68_64-darwin16, x86_64-linux-gnu,
applied to mainline,
thanks,
Iain.

gcc/testsuite/ChangeLog:

2019-10-19  Iain Sandoe  <i...@sandoe.co.uk>

        * gcc.dg/Wnonnull.c: Add attributed function declarations for
        memcpy and strlen for Darwin.

diff --git a/gcc/testsuite/gcc.dg/Wnonnull.c b/gcc/testsuite/gcc.dg/Wnonnull.c
index be89a5a755..a165baa99f 100644
--- a/gcc/testsuite/gcc.dg/Wnonnull.c
+++ b/gcc/testsuite/gcc.dg/Wnonnull.c
@@ -2,7 +2,16 @@
    { dg-do compile }
    { dg-options "-O2 -Wall" } */
 
+#ifndef __APPLE__
 #include <string.h>
+#else
+/* OSX headers do not mark up the nonnull elements yet.  */
+# include <stddef.h>
+extern size_t strlen (const char *__s)
+                     __attribute ((pure)) __attribute ((nonnull (1)));
+extern void *memcpy (void *__restrict __dest, const void *__restrict __src,
+                    size_t __n) __attribute ((nonnull (1, 2)));
+#endif
 
 char buf[100];