[SystemZ][z/OS] Use __builtin_zos_va_copy when _VARARG_EXT_ is not defined

[muiez]

Summary

z/OS has two different definitions for for va_list. The two sets of builtins are needed to support this. Need to call __builtin_zos_va_copy() when _VARARG_EXT_ is not defined. The problem only happens with c++98 or c++03.

[muiez]

Ping @libcxx @ldionne

[ldionne]

libcxx/include/__support/ibm/xlocale.h

110

Can't you enable that extension by default in C++03?

libcxx/include/__support/ibm/xlocale.h

vasprintf(char **strp, const char *fmt, va_list ap) {
   const size_t buff_size = 256;
   if ((*strp = (char *)malloc(buff_size)) == NULL) {
     return -1;
   }
 
   va_list ap_copy;
   // va_copy may not be provided by the C library in C++ 03 mode.
 #if defined(_LIBCPP_CXX03_LANG) && __has_builtin(__builtin_va_copy)
+#if defined(__MVS__) && !defined(_VARARG_EXT_)
+  __builtin_zos_va_copy(ap_copy, ap);
+#else
   __builtin_va_copy(ap_copy, ap);
+#endif
 #else
   va_copy(ap_copy, ap);
 #endif
   int str_size = vsnprintf(*strp, buff_size, fmt,  ap_copy);
   va_end(ap_copy);
 
   if ((size_t) str_size >= buff_size) {
     if ((*strp = (char *)realloc(*strp, str_size + 1)) == NULL) {