Handle fpu rounding mode at least in jits

This notably doesn't handle it in the interpreter, and out of free time to try to make that happen.

Have some test mul.s ops which I plan to add to the cpu/fpu/fpu test.

I did not notice any obvious performance impact on Android but I did not test thoroughly.  If performance does take a hit, could maybe only start setting the mode if the game ever sets the FCSR, since it's uncommon but usually done in game init if it is done.

Fixes #3988.  @thedax I am probably crazy to hope, but would love to know if Peace Walker is affected by this.

-[Unknown]