[clang] [lld] [llvm] [clang][MIPS] Add support for mipsel-windows-* targets (PR #107744)

[Martin Storsjö via cfe-commits]

https://github.com/mstorsjo commented:

I browsed through the first couple commits and added a couple pointers. Overall it looks reasonable, but things can probably be split up into even smaller commits for atomicity, which also would make it clearer where we'd want more test coverage.

https://github.com/llvm/llvm-project/pull/107744