[clang] [llvm] [mlir] [IR] Explicitly specify target feature for module asm (PR #204548)

[Nikita Popov via cfe-commits]

nikic wrote:

@efriedma-quic I've implemented a compromise where it's a string to string mapping from the perspective of the IR parser and bitcode serialization, but the supported properties are still limited and explicitly represented in-memory.

This should make it pretty easy to add extra properties, without making it a free-for-all.

https://github.com/llvm/llvm-project/pull/204548