Would this open us up to ARM Windows builds as requested in #31388 ?

MSVC has many issues, for example:

Another one:

• Non-compilant pre-processor: 5db1958 from #29256. Though it looks like we could work around this with /Zc:preprocessor

Am agnostic on this issue though. I could imagine benefits to compiler diversity like ensuring is more portable, or finding bugs missed by other compilers, or allowing more developer tools to be used. But those things might not apply here.

Also #31158?

I could imagine benefits to compiler diversity like ensuring is more portable, or finding bugs missed by other compilers, or allowing more developer tools to be used.

Good point. I guess the only portability issues or bugs were found by using the msSTL, so using clang+msSTL should be fine. If there are real bugs found by msvc (or tools that only work with msvc), it would be good to list them in this brainstorming issue. Otherwise, the reasoning seems recursive, to write portable code to support msvc, for the only reason that msvc can be supported.