[clang] [llvm] [Driver][DirectX] Add `/Qembed_debug` and `/Fd` flags (PR #204166)

[Vladislav Dzhidzhoev via cfe-commits]

dzhidzhoev wrote:

> * For (1), this is very much like `-split-dwarf`. IMO, we should probably generalize `MCTargetOptions::SplitDwarfFile` to `SplitDebugFile` and implement `/Fd` generally. Doing this in a "this just forwards to a DirectX target option" way is adding tech debt, and ignores the fact that this option is much more general than just DirectX. Supporting this improves MSVC compatibility and also helps with what to do for things like HLSL targeting SPIR-V.

Maybe @rnk could suggest whether there is interest in `/Fd`, `/Zi` options in clang-cl. 

https://github.com/llvm/llvm-project/pull/204166