x86jit: Avoid MOVSS into self.
x86jit: Add a MAP_NOLOCK flag to not lock.

Only for MapRegs*.  And then lock all by default, including
TryMapRegsVS().
x86jit: Improve spilling in vf2i.

This should improve which ones we spill on 32 bit at least.
Merge pull request #7120 from unknownbrackets/jit-simd

x86jit: Add a MAP_NOLOCK flag