Disable -Wstringop-overread for some string tests

[Joseph Myers]

Similarly to Maciej's changes to fix the build of rawmemchr in the
presence of GCC 11's -Wstringop-overread, also disable that option in
two string function tests that have similar warnings and other string
function warnings already disabled.

Tested with build-many-glibcs.py for aarch64-linux-gnu and
arm-linux-gnueabi that it fixes building the glibc testsuite.

diff --git a/string/tester.c b/string/tester.c
index bcd7148c2e..b7acf29c81 100644
--- a/string/tester.c
+++ b/string/tester.c
@@ -47,6 +47,9 @@ DIAG_IGNORE_NEEDS_COMMENT (7, "-Wstringop-overflow=");
 #if __GNUC_PREREQ (8, 0)
 DIAG_IGNORE_NEEDS_COMMENT (8, "-Wstringop-truncation");
 #endif
+#if __GNUC_PREREQ (11, 0)
+DIAG_IGNORE_NEEDS_COMMENT (11, "-Wstringop-overread");
+#endif
 
 
 #define	STREQ(a, b)	(strcmp((a), (b)) == 0)
diff --git a/string/tst-cmp.c b/string/tst-cmp.c
index 13af0fcb83..e73025cfdf 100644
--- a/string/tst-cmp.c
+++ b/string/tst-cmp.c
@@ -104,6 +104,10 @@ strncmp_max (const char *left, const char *right)
   /* 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
+#if __GNUC_PREREQ (11, 0)
+  /* Likewise GCC 11, with a different warning option.  */
+  DIAG_IGNORE_NEEDS_COMMENT (11, "-Wstringop-overread");
 #endif
   return strncmp (left, right, SIZE_MAX);
   DIAG_POP_NEEDS_COMMENT;
@@ -117,6 +121,10 @@ strncasecmp_max (const char *left, const char *right)
   /* 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
+#if __GNUC_PREREQ (11, 0)
+  /* Likewise GCC 11, with a different warning option.  */
+  DIAG_IGNORE_NEEDS_COMMENT (11, "-Wstringop-overread");
 #endif
   return strncasecmp (left, right, SIZE_MAX);
   DIAG_POP_NEEDS_COMMENT;

-- 
Joseph S. Myers
joseph@codesourcery.com