[clang] [Matrix] Add a row\col major toggle in the clang driver (PR #167628)

[Justin Bogner via cfe-commits]

https://github.com/bogner approved this pull request.

This all looks reasonable and correct to me. It'd be good to get an acknowledgement from @cofibrant that all of their concerns have been addressed.

https://github.com/llvm/llvm-project/pull/167628