Remove EMX_MAKEFILE (add EMX support to Makefile.direct)

Remove EMX_MAKEFILE (add EMX support to Makefile.direct)

* EMX_MAKEFILE: Remove.
* Makefile.am (EXTRA_DIST): Remove EMX_MAKEFILE entity.
* Makefile.direct (OTHER_MAKEFILES): Likewise.
* Makefile.direct (CC, RANLIB): Add comment for EMX target.
* Makefile.direct (EXEEXT): New variable (empty by default).
* Makefile.direct (UTILS, all, cords, test_cpp, check-cpp, c++-t,
dyn_test, cord/cordtest, cord/de, if_mach, threadlibs, if_not_there,
gctest, setjmp_test, check): Add $(EXEEXT) suffix to if_mach,
if_not_there, threadlibs, gctest, cord/cordtest, test_cpp, cord/de,
setjmp_test.