[clang] [llvm] [inlineasm] Add special support for "rm" inline asm constraints (PR #181973)

[Bill Wendling via cfe-commits]

bwendling wrote:

Created https://github.com/llvm/llvm-project/pull/195592, which is a simpler implementation that focuses on modifying the front-end to favor 'r' over 'm' for `-O[1-3]` and changing the SelectionDAG builder to find the best option. PTAL

https://github.com/llvm/llvm-project/pull/181973