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

[vries at gcc dot gnu.org]

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

--- Comment #18 from vries at gcc dot gnu.org ---
Created attachment 39484
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=39484&action=edit
Tentative patch using attributes ms_abi/sysv_abi

not build or regression tested yet, but at least makes test-case pass.