Updated regressions with tests
Bring correct operands to registers as required

This fixes incorrect asm generation for certain ops
Fixed out_dup - REG and FLAG need handling
Fixed vtop_clear use when vtop wasn't the target
Fixed signed not being set on a type
Fixed off-by-one causing dodgy stack_sz

Also changed reserved_regs to be unsigned char array since we don't need
N ints of space.
COW for register duplication todo
Brought mips backend into line
Use immediate instructions if possible