[clang] [clang] Add -mlarge-eh-encoding driver flag (PR #187583)

[Farid Zakaria via cfe-commits]

fzakaria wrote:

> Yes, exposing `RegisterMCTargetOptionsFlags` to clang seems reasonable. Some research is needed to figure out the value precedence with multiple sources.

Looks actually doable. I put up https://github.com/llvm/llvm-project/pull/210087
There is a test that shows the precedence is working: clang > `-mllvm`

https://github.com/llvm/llvm-project/pull/187583