12705 remove __builtin_alloca() declaration from string.h

@@ -20,10 +20,11 @@
  */
 
 /*
  * Copyright 2014 Garrett D'Amore <garrett@damore.org>
  * Copyright (c) 1989, 2010, Oracle and/or its affiliates. All rights reserved.
+ * Copyright 2020 Joyent, Inc.
  */
 
 /*      Copyright (c) 1988 AT&T */
 /*        All Rights Reserved   */
 

@@ -137,18 +138,13 @@
 extern char *strdup(const char *);
 #endif
 
 #if defined(__EXTENSIONS__) || \
         (!defined(_STRICT_STDC) && !defined(__XOPEN_OR_POSIX))
+
 #if defined(__GNUC__)
 
-/*
- * gcc provides this inlining facility but Studio C does not.
- * We should use it exclusively once Studio C also provides it.
- */
-extern void *__builtin_alloca(size_t);
-
 #define strdupa(s)                                                      \
         (__extension__(                                                 \
         {                                                               \
         char *__str = (char *)(s);                                      \
         strcpy((char *)__builtin_alloca(strlen(__str) + 1), __str);     \