Checking the register implicitly covers checking for a data mode.

This flag is plain redundant.

It returns a null pointer instead of a ia32_NoReg_GP.

This avoids the custom emitter, which just duplicated what the generic machinery does.

Some callers did not handle it.
They cannot be permuted (e.g. Jcc).

ia32: Use arch_get_irn_register() instead of arch_get_irn_register_in() where the operand is already available.

The noreg is always different to any output register.

Register outputs always need the mode of the register class involved.

Also adds a new INSN_MODE_INVALID for 0 to catch uninitialized values.

I found this neat trick in llvm output, and the existing code was broken
anyway.

ir: Use mode_is_float()/mode_is_int() instead of get_mode_sort()/->sort == irms_float_number/irms_int_number.

There are still similar problems left.