ia64: Remove bzero optimization

The symbol is not present current POSIX specification and compiler
already generates memset call.  The arch specific implementation
is just to avoid the __bzero symbol creation (which ia64 abi does
not export).

string/bzero.c

@@ -17,12 +17,12 @@
 
 #include <string.h>
 
-#undef __bzero
-
 /* Set N bytes of S to 0.  */
 void
 __bzero (void *s, size_t len)
 {
   memset (s, '\0', len);
 }
+#ifndef __bzero
 weak_alias (__bzero, bzero)
+#endif