Fixes for when the host WIN32, but not MSC.
* complete.c: Sometimes have pwd.h
* parens.c: WIN32 has similar restrictions to __GO32__.
* readline.c (__GO32__): Some of this moved into rldefs.h
* signals.c (__GO32__): Likewise.
* rldefs.h (MSDOS||WIN32) becomes MSDOS||MSC.
(WIN32&&!WIN32): New definitions.
