[COMMITTED 2.32] Remove __warn_memset_zero_len [BZ #25399]

[Siddhesh Poyarekar <siddhesh@sourceware.org>]

Non-gcc compilers (clang and possibly other compilers that do not
masquerade as gcc 5.0 or later) are unable to use
__warn_memset_zero_len since the symbol is no longer available on
glibc built with gcc 5.0 or later.  While it was likely an oversight
that caused this omission, the fact that it wasn't noticed until
recently (when clang closed the gap on _FORTIFY_SUPPORT) that the
symbol was missing.

Given that both gcc and clang are capable of doing this check in the
compiler, drop all remaining signs of __warn_memset_zero_len from
glibc so that no more objects are built with this symbol in future.

(cherry-picked from dc274b141666766b8ef70992d887e3c0c5e41bed)
---
 string/bits/string_fortified.h | 15 ---------------
 1 file changed, 15 deletions(-)

diff --git a/string/bits/string_fortified.h b/string/bits/string_fortified.h
index 309d0f39b2..c8d3051af8 100644
--- a/string/bits/string_fortified.h
+++ b/string/bits/string_fortified.h
@@ -22,11 +22,6 @@
 # error "Never use <bits/string_fortified.h> directly; include <string.h> instead."
 #endif
 
-#if !__GNUC_PREREQ (5,0)
-__warndecl (__warn_memset_zero_len,
-	    "memset used with constant zero length parameter; this could be due to transposed parameters");
-#endif
-
 __fortify_function void *
 __NTH (memcpy (void *__restrict __dest, const void *__restrict __src,
 	       size_t __len))
@@ -58,16 +53,6 @@ __NTH (mempcpy (void *__restrict __dest, const void *__restrict __src,
 __fortify_function void *
 __NTH (memset (void *__dest, int __ch, size_t __len))
 {
-  /* GCC-5.0 and newer implements these checks in the compiler, so we don't
-     need them here.  */
-#if !__GNUC_PREREQ (5,0)
-  if (__builtin_constant_p (__len) && __len == 0
-      && (!__builtin_constant_p (__ch) || __ch != 0))
-    {
-      __warn_memset_zero_len ();
-      return __dest;
-    }
-#endif
   return __builtin___memset_chk (__dest, __ch, __len, __bos0 (__dest));
 }
 
-- 
2.26.2