[clang] [clang][Driver] Support passing arbitrary args to -cc1as with -Xclangas. (PR #100714)

[Fangrui Song via cfe-commits]

MaskRay wrote:


> This is one of the ideas I gave in https://github.com/llvm/llvm-project/issues/97517. I opted to propose this one first as introducing a new -Xclangas option comes with no concerns about GCC compatibility as with -Xassembler.

Please update the description/commit message to include the justification in a formal way.


https://github.com/llvm/llvm-project/pull/100714