Integer round inf/nan to INT_MAX/INT_MIN.

Instead of 0x80000000 (the default "invalid" value.)
Improves the fpu test.
Don't say nan is equal to anything.

I guess we were passing this because of fastmath?  Fixes interpreter
cpu/fpu/fpu test on Windows anyway.
Check for nan/inf in trunc.w.s in x86 jit.

Now x86 jit passes the fpu test too.
Merge pull request #3760 from unknownbrackets/mips-minor

Fix fpu non-finite rounding on x86