[CIR] Upstream TBAA handling

[andykaylor]

Overview

Upstream support for generating TBAA attributes and lowering to TBAA metadata in LLVM IR.

We should carefully consider how we can reuse/share the classic codegen implementation for generating TBAA metadata.

Suggested minimal test case

// Compile with -O1
void test_int(int *a) {
  a = 1;
}

Existing incubator tests

clang/test/CIR/CodeGen/tbaa-bitinit.c
clang/test/CIR/CodeGen/tbaa-enum.c
clang/test/CIR/CodeGen/tbaa-enum.cpp
clang/test/CIR/CodeGen/tbaa-pointer.cpp
clang/test/CIR/CodeGen/tbaa-scalar.c
clang/test/CIR/CodeGen/tbaa-struct.cpp
clang/test/CIR/CodeGen/tbaa-union.cpp
clang/test/CIR/CodeGen/tbaa-vptr.cpp