Similarly to PR #39, this reduces the amount of duplication between makefiles. The MinGW and DJGPP makefiles haven't been tested, but should work fine. In addition, I don't know enough about AMU or Borland's make, so I left those makefiles alone.
I've merged this one from the diff file. It builds fine on Linux and MinGW via Cygwin. The other environments are ones I don't have the means to build, maybe @jgharston has this?
Similarly to PR #39, this reduces the amount of duplication between makefiles. The MinGW and DJGPP makefiles haven't been tested, but should work fine. In addition, I don't know enough about AMU or Borland's make, so I left those makefiles alone.