armjit: Spill an imm armreg back to an imm.

We might be able to avoid the store or etc.
armjit: Report some unexpected situations.
armjit: Prioritize spilling regs not used soon.

This may improve trashing.
x86jit: Refactor and skip flushes in branch cont.

Still not faster, but at least the code isn't as messy.
Merge pull request #4516 from unknownbrackets/armjit-minor

Improve spilling regs on ARM