Build fix

I was getting the following error:
src/osd/retro/retromain.c:386:35: fatal error: ../portmedia/pmmidi.inc: No such file or directory
 #include "../portmedia/pmmidi.inc"

Putting the file back in only causes link errors with libemu.a from osdcore.c.
Commenting out those two lines allows MAME to build and from my testing seems to work ok.