[Bug lto/70955] [6/7 Regression] Wrong code generation for __builtin_ms_va_list with -flto

[steven.shi at intel dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70955

--- Comment #16 from Steven Shi <steven.shi at intel dot com> ---
How to checkout the 6.3 code from GCC trunk? I hope to verify this fix on Uefi
firmware GCC LTO build.