[2.27 COMMITTED] <string.h>: Define __CORRECT_ISO_CPP_STRING_H_PROTO for Clang [BZ #25232]

[2.27 COMMITTED] <string.h>: Define __CORRECT_ISO_CPP_STRING_H_PROTO for Clang [BZ #25232]

[Dmitry V. Levin]

From: Kamlesh Kumar <kamleshbhalui@gmail.com>

Without the asm redirects, strchr et al. are not const-correct.

libc++ has a wrapper header that works with and without
__CORRECT_ISO_CPP_STRING_H_PROTO (using a Clang extension).  But when
Clang is used with libstdc++ or just C headers, the overloaded functions
with the correct types are not declared.

This change does not impact current GCC (with libstdc++ or libc++).

(cherry picked from commit 953ceff17a4a15b10cfdd5edc3c8cae4884c8ec3)
---
 NEWS            | 1 +
 string/string.h | 3 ++-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/NEWS b/NEWS
index f426f29fe4..40c9e23d10 100644
--- a/NEWS
+++ b/NEWS
@@ -153,6 +153,7 @@ The following bugs are resolved with this release:
   [24744] io: Remove the copy_file_range emulation
   [25203] libio: Disable vtable validation for pre-2.1 interposed handles
   [25204] Ignore LD_PREFER_MAP_32BIT_EXEC for SUID programs
+  [25232] No const correctness for strchr et al. for Clang++
 
 \f
 Version 2.27
diff --git a/string/string.h b/string/string.h
index 150cfd8b13..22cd0fa08f 100644
--- a/string/string.h
+++ b/string/string.h
@@ -33,7 +33,8 @@ __BEGIN_DECLS
 #include <stddef.h>
 
 /* Tell the caller that we provide correct C++ prototypes.  */
-#if defined __cplusplus && __GNUC_PREREQ (4, 4)
+#if defined __cplusplus && (__GNUC_PREREQ (4, 4) \
+			    || __glibc_clang_prereq (3, 5))
 # define __CORRECT_ISO_CPP_STRING_H_PROTO
 #endif
 
-- 
ldv