windows tests fixes

Ok, so enabling EMIT_X86 works for mingw but nor for msvc: other preprocessor definitions are used but even after fixing that it's still does not compile because emitnative.c requires nlr_pop/push to be functions. After making them functions uPy builds but all native code samples segfault. So that means there's not only an os distinction to be made but also a 'compiled by'. While that is doable, it seems way out of scope of run-tests so @pfalcon's proposal (or something with that principle) is the only thing that is going to work here. I'll remove the last line and see what fix comes out of #861