The windows-msvc target is meant to be ABI compatible with MSVC,
including the exception handling. Ensure that a windows-msvc triple
always equates to the MSVC personality being used.
This mostly affects the GNUStep and ObjFW Obj-C runtimes. To the best of
my knowledge, those are normally not used with windows-msvc triples. I
believe WinObjC is based on GNUStep (or it at least uses libobjc2), but
that also takes the approach of wrapping Obj-C exceptions in C++
exceptions, so the MSVC personality function is the right one to use
there as well.
I guess previously we carefully arranged to go to whatever the regular objc personality would be, but we're not doing that now with funclet windows eh.
Maybe we could drastically simplify this by checking for an msvc environment and seh before checking each language?