LLVM: Stop llvm saving stg caller-save regs across C calls
This is already handled by the Cmm code generator so LLVM is simply duplicating work. LLVM also doesn't know which ones are actually live so saves them all which causes a fair performance overhead for C calls on x64. We stop llvm saving them across the call by storing undef to them just before the call.
Showing with 30 additions and 9 deletions