fix stack probe lowering for x86_intrcc

The x86_intrcc calling convention will build two STACKALLOC_W_PROBING machine instructions if the function takes an error code. This is caused by an additional call to emitSPUpdate in llvm/lib/Target/X86/X86FrameLowering.cpp:1650. Previously only the first STACKALLOC_W_PROBING machine instruction was properly handled, the second one was simply ignored. This lead to miscompilations where the stack pointer wasn't properly updated (see https://github.com/rust-lang/rust/issues/109918). This patch fixes this by handling all STACKALLOC_W_PROBING machine instructions.

To be honest I don't quite understand why this didn't lead to more noticeable miscompilations previously.

This is my first time contributing to LLVM.

Reviewed By: pengfei

Differential Revision: https://reviews.llvm.org/D150033