armjit: keep track of instructions in jitstate.

To match x86.
armjit: Copy over (disabled) immbranch optim.

This does a little loop unrolling.  Costs a bit more cache space, but
avoids flushing regs for longer.

Not enabled.
x86/armjit: Add jump following (off by default.)

Inlines function calls up to a certain extent.  Allows us to get
immediates all the way to a syscall, for example, usually.

Not sure if faster.
x86jit: Rename imm funcs to match armjit.