Make the Makefile more portable
Removes some GNUisms in favor of POSIX-make or generally more portable make constructs. This does not (yet) remove all GNU-isms, but I thought it might be worth looking at in case it's something we want to do (of course, maybe it's not as GNUMake works fine for most people).
Signed-off-by: Sam Whited sam@samwhited.com