[clang] [UEFI] X86_64 UEFI Clang Driver (PR #76838)

[Fangrui Song via cfe-commits]

MaskRay wrote:

Some older toolchains were probably contributed with a lot of `CmdArgs.push_back` uncovered by tests. They are not good examples to follow. For new toolchains, we do want all constructed `CmdArgs.push_back` to be covered. This allows refactoring by someone who is unfamiliar with your usage pattern.

https://github.com/llvm/llvm-project/pull/76838