[MIR] MSVC unwinding instructions unimplemented

[alexcrichton]

In #30448 LLVM is being upgraded for the purpose of using the new exception handling instructions to implement SEH unwinding for MSVC on both 32 and 64-bit platforms. This support involves translating invoke instructions and landing pads differently (e.g. modifications to trans), but these changes have not yet been ported over to the MIR trans just yet.

For now I'm going to ignore the MIR tests on MSVC which ensure that landing pads are working, but this'll track the implementation in MIR of the MSVC unwinding instructions.

cc @nagisa

[nagisa]

I have plans to implement these, but won’t begin working on these before Monday.

[nagisa]

This is fixed.