[Bug target/50818] va_list is filled incorrectly in functions with ms_abi attribute on amd64

[hjl.tools at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=50818

--- Comment #7 from H.J. Lu <hjl.tools at gmail dot com> ---
As a workaround, you can try

  __builtin_ms_va_list ap;
  __builtin_ms_va_start (ap, n);
  __builtin_ms_va_end (ap);

instead of

  __builtin_va_list ap;
  __builtin_va_start (ap, n);
  __builtin_va_end (ap);