[clang] [LinkerWrapper] Add an overriding option for debugging (PR #91984)

[Yaxun Liu via cfe-commits]

yxsamliu wrote:

would it be more useful to allow swapping the output by environment variable and MD5 hash, e.g.

CLANG_LINK_WRAPPER_SWAP_OUTPUT=hash1:file1,hash2:file2

it calculates the MD5 hash of the output file, if matching, swap it with the specified file. This way, we can set an env var to swap any linker wrapper output in a normal build. 

https://github.com/llvm/llvm-project/pull/91984