[PATCH v2] string: Fix GCC 11 `-Werror=stringop-overread' error

["Maciej W. Rozycki" <macro@wdc.com>]

Fix a compilation error:

In function '__rawmemchr',
    inlined from '__rawmemchr' at rawmemchr.c:27:1:
rawmemchr.c:36:12: error: 'memchr' specified bound 18446744073709551615 exceeds maximum object size 9223372036854775807 [-Werror=stringop-overread]
   36 |     return memchr (s, c, (size_t)-1);
      |            ^~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
../o-iterator.mk:9: recipe for target '.../string/rawmemchr.o' failed

introduced with GCC 11 commit d14c547abd48 ("Add -Wstringop-overread 
for reading past the end by string functions.").
---
Changes from v1:

- Wrap the pragma into `__GNUC_PREREQ (11, 0)'.
---
 string/rawmemchr.c |    4 ++++
 1 file changed, 4 insertions(+)

glibc-stringop-overread.diff
Index: glibc/string/rawmemchr.c
===================================================================
--- glibc.orig/string/rawmemchr.c
+++ glibc/string/rawmemchr.c
@@ -32,6 +32,10 @@ RAWMEMCHR (const void *s, int c)
      PTRDIFF_MAX; the use of SIZE_MAX is deliberate here.  */
   DIAG_IGNORE_NEEDS_COMMENT (8, "-Wstringop-overflow=");
 #endif
+#if __GNUC_PREREQ (11, 0)
+  /* Likewise GCC 11, with a different warning option.  */
+  DIAG_IGNORE_NEEDS_COMMENT (11, "-Wstringop-overread");
+#endif
   if (c != '\0')
     return memchr (s, c, (size_t)-1);
   DIAG_POP_NEEDS_COMMENT;