[clang] Add Swift support for MIPS

[colemancda]

Adds support for compiling Swift targeting the MIPS ABI

Differential Revision: https://reviews.llvm.org/D137512

Resolves SR-15943

[CodaFi]

Does this have a corresponding LLVM patch up for review?

[colemancda]

No, sorry.

[CodaFi]

I would ask that you upstream these. The next branch here is intended to be a staging area for commits that come directly from LLVM before we settle on a stable version. In general, we merge Swift-specific commits into the stable branch (which, as of this writing is stable/20211026) and make good faith effort to upstream these patches so they are automatically included in next when we retag things.

[colemancda]

@CodaFi Any suggestions on who I should contact at LLVM or assign to get this merged?

https://reviews.llvm.org/D137512

[CodaFi]

I will ping maintainers about this tomorrow morning. This looks pretty good to me, but I'm far from the expert in Clang infra we have for different target infos.

[CodaFi]

@swift-ci test

[aschwaighofer]

Can you rebase https://reviews.llvm.org/D137512 on top of github.com:apple/llvm-project.git's main?

[colemancda]

@aschwaighofer Rebased off github.com:apple/llvm-project.git llvm.org/main branch. There is no main branch in that repo.