Add LLVM based MinGW targets

[mati865]

Rust PR: rust-lang/rust#94872

[dot-asm]

This is duplicate of comment at rust-lang

Not that my word weighs a lot here and I apologize, but I fail to see the need for an additional target. Is there a programming interface that clang uses/requires that gcc and/or Microsoft cl don't? What I'm trying to say is that it's rather the programming interface that defines any particular target platform, not the compiler. Compilers are supposed to be and actually are interchangeable. For example, on Windows you can use clang-cl instead of vendor cl with *-msvc targets. On Linux you can freely switch between clang and gcc. And I see no reason for why it would be impossible to have the similar arrangement for *-windows-gnu targets.

[dot-asm]

Just in case for reference, my remark was refuted in the referred thread at rust-lang. To summarize, it boils down to irreconcilable differences in exception handling mechanisms.

[thomcc]

I'm in favor of supporting the -gnullvm targets, but this seems to remove one of the -gnu targets?

[mati865]

Possibly due to repo move GitHub ignores pushes to this branch, moving to new PR: #734