Fix tst-cmp.c build with GCC mainline.

Building the testsuite with GCC mainline fails with
-Wstringop-overflow= errors in string/tst-cmp.c.  These are for calls
to strncmp and strncasecmp with SIZE_MAX size argument.  The tests are
deliberately using this size that would be dubious in normal code, so
this patch disables the warning for the calls in question.

Tested with build-many-glibcs.py for aarch64-linux-gnu.

	* string/tst-cmp.c: Include <libc-diag.h>.
	(strncmp_max): Disable -Wstringop-overflow= around call to
	strncmp.
	(strncasecmp_max): Disable -Wstringop-overflow= around call to
	strncasecmp.

1 files changed, 15 insertions, 0 deletions

diff --git a/string/tst-cmp.c b/string/tst-cmp.c
index 1a7f1c8b89..3b9f7b2506 100644
--- a/string/tst-cmp.c
+++ b/string/tst-cmp.c
@@ -26,6 +26,7 @@
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>
+#include <libc-diag.h>
 
 static int
 signum (int val)
@@ -98,13 +99,27 @@ strncasecmp_64 (const char *left, const char *right)
 static int
 strncmp_max (const char *left, const char *right)
 {
+  DIAG_PUSH_NEEDS_COMMENT;
+#if __GNUC_PREREQ (7, 0)
+  /* GCC 9 warns about the size passed to strncmp being larger than
+     PTRDIFF_MAX; the use of SIZE_MAX is deliberate here.  */
+  DIAG_IGNORE_NEEDS_COMMENT (9, "-Wstringop-overflow=");
+#endif
   return strncmp (left, right, SIZE_MAX);
+  DIAG_POP_NEEDS_COMMENT;
 }
 
 static int
 strncasecmp_max (const char *left, const char *right)
 {
+  DIAG_PUSH_NEEDS_COMMENT;
+#if __GNUC_PREREQ (7, 0)
+  /* GCC 9 warns about the size passed to strncasecmp being larger
+     than PTRDIFF_MAX; the use of SIZE_MAX is deliberate here.  */
+  DIAG_IGNORE_NEEDS_COMMENT (9, "-Wstringop-overflow=");
+#endif
   return strncasecmp (left, right, SIZE_MAX);
+  DIAG_POP_NEEDS_COMMENT;
 }
 
 int