add follow-up assert during unwinding

[kunalspathak]

follow-up to #112799 (comment)

Copilot wasn't able to review any files in this pull request.

Files not reviewed (1)

• src/coreclr/jit/unwindamd64.cpp: Language not supported

[kunalspathak]

@BruceForstall @tannergooding

[dotnet-policy-service]

Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch
See info in area-owners.md if you want to be subscribed.

[tannergooding]

I think @BruceForstall was also suggesting we validate that it's within the expected range to cover future expansions we might have

So we currently have up to 32 for both float and integer registers.

[BruceForstall]

Yeah, I was thinking something like:

        unsigned unwindRegNum;
        if (genIsValidFloatReg(reg))
        {
            unwindRegNum = reg - XMMBASE;
        }
        else
        {
            assert(genIsValidIntReg(reg));
            unwindRegNum = reg;
        }
        assert(unwindRegNum <= 15);
        code->OpInfo = (UCHAR)unwindRegNum;
        assert((unsigned)code->OpInfo == unwindRegNum); // check that it fit