[2.26 COMMITTED] Disable strncat test array-bounds warnings for GCC 8.

[fweimer@redhat.com (Florian Weimer)]

From: Joseph Myers <joseph@codesourcery.com>

Some strncat tests fail to build with GCC 8 because of -Warray-bounds
warnings.  These tests are deliberately test over-large size arguments
passed to strncat, and already disable -Wstringop-overflow warnings,
but now the warnings for these tests come under -Warray-bounds so that
option needs disabling for them as well, which this patch does (with
an update on the comments; the DIAG_IGNORE_NEEDS_COMMENT call for
-Warray-bounds doesn't need to be conditional itself, because that
option is supported by all versions of GCC that can build glibc).

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

	* string/tester.c (test_strncat): Also disable -Warray-bounds
	warnings for two tests.

(cherry picked from commit 1421f39b7eadd3b5fbd2a3f2da1fc006b69fbc42)

2017-12-18  Joseph Myers  <joseph@codesourcery.com>

	* string/tester.c (test_strncat): Also disable -Warray-bounds
	warnings for two tests.

diff --git a/string/tester.c b/string/tester.c
index 66b11515b0..02ea8e1e16 100644
--- a/string/tester.c
+++ b/string/tester.c
@@ -387,9 +387,11 @@ test_strncat (void)
   DIAG_PUSH_NEEDS_COMMENT;
 #if __GNUC_PREREQ (7, 0)
   /* GCC 7 warns about the size passed to strncat being larger than
-     the size of the buffer; this is deliberately tested here..  */
+     the size of the buffer; this is deliberately tested here; GCC 8
+     gives a -Warray-bounds warning about this.  */
   DIAG_IGNORE_NEEDS_COMMENT (7, "-Wstringop-overflow=");
 #endif
+  DIAG_IGNORE_NEEDS_COMMENT (8, "-Warray-bounds");
   (void) strncat (one, two, 99);
   DIAG_POP_NEEDS_COMMENT;
   equal (one, "ghef", 5);			/* Basic test encore. */
@@ -480,9 +482,11 @@ test_strncat (void)
 #if __GNUC_PREREQ (7, 0)
 	    /* GCC 7 warns about the size passed to strncat being
 	       larger than the size of the buffer; this is
-	       deliberately tested here..  */
+	       deliberately tested here; GCC 8 gives a -Warray-bounds
+	       warning about this.  */
 	    DIAG_IGNORE_NEEDS_COMMENT (7, "-Wstringop-overflow=");
 #endif
+	    DIAG_IGNORE_NEEDS_COMMENT (8, "-Warray-bounds");
 	    check (strncat (buf1 + n2, buf2 + n1, ~((size_t) 0) - n4)
 		   == buf1 + n2, ntest);
 	    DIAG_POP_NEEDS_COMMENT;