Propagate --num-imag-ptr choices to object files about llvm-mos

[johnwbyrd]

Maybe a severe linker warning will be enough. There may be some scenarios where it's ok to mix different --num-imag-ptr settings, but at least the user needs to know that the code PROBABLY will not run.

[mysterymath]

We probably shouldn't allow people to mix num-imag-ptr settings for now. If interrupt code is ever going to work well, we'll probably need a compiler annotations for marking functions with num-imag-ptr. This would make it fairly easy to carve out the interrupt handler routines in C itself. We'd also be able to emit compiler errors whenever a function with a lower num-imag-ptr directly calls a function with a higher num-imag-ptr.

[mysterymath]

The calling convention is now stable regardless of the number of imaginary pointers used. Accordingly, there's no longer any danger of mixing object files compiled with differing numbers of imaginary pointers.