JIT: don't rely on undefined behavior for constant overflow checking

[FioraAeterna]

I have no idea what the compiler does with these, and this code probably
isn't triggered in most games, but it's probably better not to taunt the
undefined behavior demon.

[Tilka]

lgtm if you add #include <limits>.

[Sonicadvance1]

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[comex]

That's really ugly. A good compiler will optimize (s64)(i - j) != (s64)i - (s64)j (where i and j are signed) to false. However, to correctly avoid undefined behavior you also need to modify the lines that compute the values, e.g. gpr.SetImmediate32(d, i + j); should have the argument changed to (s32) ((u32) i + (u32) j)).

(Not to butt in too much, but I'd also prefer it if you didn't use the same name, GenerateConstantOverflow, for a different function.)