[CIR] Upstream support for inline assembly

[andykaylor]

Overview

Upstream support for handling inline assembly in ClangIR.

The ClangIR incubator repository has about 600 lines of code to process inline asm statements in the clang/lib/CIR/CodeGen/CIRAsm.cpp file. That will need to be moved in smaller pieces for effective review.

Suggested minimal test case

void f1() {
  __asm__ volatile("" : : : );
}

Existing incubator tests

Also in the incubator, clang/test/CIR/CodeGen/asm.c contains test cases for GCC syntax assembly.