New frsqrte implementation; verified accurate.

This is similar to the old implementation, but it uses smaller tables, and
handles more edge cases correctly.  (hwtest coming soon.)
Jit: Use infinity and NaN from numeric_limits.

MSVC's implementation of INFINITY is unusable.
Jit: remove ARM implementations of fres and frsqrte.

Like the x86 implementations, they simply aren't correct.