[2.26 COMMITTED] Ignore -Wrestrict for one strncat test.

[fweimer@redhat.com (Florian Weimer)]

From: Joseph Myers <joseph@codesourcery.com>

With current GCC mainline, one strncat test involving a size close to
SIZE_MAX results in a -Wrestrict warning that that buffer size would
imply that the two buffers must overlap.  This patch fixes the build
by adding disabling of -Wrestrict (for GCC versions supporting that
option) to the already-present disabling of -Wstringop-overflow= and
-Warray-bounds for this test.

Tested with build-many-glibcs.py that this restores the testsuite
build with GCC mainline for aarch64-linux-gnu.

	* string/tester.c (test_strncat) [__GNUC_PREREQ (7, 0)]: Also
	ignore -Wrestrict for one test.

(cherry picked from commit 35ebb6b0c48bc671d9c54e089884f9bf6fca540e)

2018-06-14  Joseph Myers  <joseph@codesourcery.com>

	* string/tester.c (test_strncat) [__GNUC_PREREQ (7, 0)]: Also
	ignore -Wrestrict for one test.

diff --git a/string/tester.c b/string/tester.c
index 02ea8e1e16..8fdbe3de13 100644
--- a/string/tester.c
+++ b/string/tester.c
@@ -485,6 +485,10 @@ test_strncat (void)
 	       deliberately tested here; GCC 8 gives a -Warray-bounds
 	       warning about this.  */
 	    DIAG_IGNORE_NEEDS_COMMENT (7, "-Wstringop-overflow=");
+	    /* GCC 9 as of 2018-06-14 warns that the size passed is
+	       large enough that, if it were the actual object size,
+	       the objects would have to overlap.  */
+	    DIAG_IGNORE_NEEDS_COMMENT (9, "-Wrestrict");
 #endif
 	    DIAG_IGNORE_NEEDS_COMMENT (8, "-Warray-bounds");
 	    check (strncat (buf1 + n2, buf2 + n1, ~((size_t) 0) - n4)