jit: Rename the rounding mode funcs to clarify.

They apply/restore the value, set/clear is confusing.
jit: Avoid applying/restoring the rounding mode.

If the game never sets it, we can skip around syscalls, interpreter,
replacements, etc.
x86jit: Fix force flush to zero.
jit: Reorganize imm branch logic a bit.
jit: Statically jump for fixed branches.

This handles both loops (first step is known) and static branches (some
code uses them instead of jumps, and we disassemble that to "b".)

Not likely to be a big improvement, but might help if the branch predictor
was wrong.

This is as opposed to continuing, which would build a larger jit block.
x86jit: Fix a bug in branch continuing.

When we predict it won't take a likely delay slot, we'd lose our register
allocation state.
Skip setting a0 in the idle thread.

We don't need the param for our fake syscall.  This is safe since it's all
savestated.
Merge pull request #6997 from unknownbrackets/jit-minor

Avoid emitting rounding mode code when not needed