This means llvm-mc should now build without depending on the target
CodeGen libraries.
Fix up a few includes in RISCV, AMDGPU, and X86 MCA to avoid transitive
deps on CodeGen.
Fixes#64166
memory-barrier instructions to providing targets and developers a convenient
way to explicitly declare which instructions are memory-barriers.
Differential Revision: https://reviews.llvm.org/D116779