ddb306ab57
This patch adds a Clang-compatible -mtune option to opt, following up the addition to llc: https://github.com/llvm/llvm-project/pull/186998, to enable decoupled ISA and microarchitecture targeting. Example use case is `MaxInterleaveFactor` for the loop vectorizer. The implementation registers the new codegen flag for opt, which consumes it and sets tune-cpu attributes for functions to be consumed by the backend.