Flip HAVE_OPENMPT on by default for non-Windows makefile

src/Makefile

@@ -74,8 +74,7 @@
 #     Compile without BSD API, add 'NONET=1'
 #     Compile without IPX/SPX, add 'NOIPX=1'
 #     Compile Mingw/SDL with S_DS3S, add 'DS3D=1'
-#     Compile without libopenmpt on Windows, add 'NOOPENMPT=1'
-#     Compile with libopenmpt on other platforms, add 'OPENMPT=1'
+#     Compile without libopenmpt, add 'NOOPENMPT=1'
 #     Compile with S_FMOD3D, add 'FMOD=1' (WIP)
 #     Compile with S_OPENAL, add 'OPENAL=1' (WIP)
 #     To link with the whole SDL_Image lib to load Icons, add 'SDL_IMAGE=1' but it isn't not realy needed
@@ -184,15 +183,9 @@ ifdef DJGPPDOS
 include djgppdos/Makefile.cfg
 endif
 
-ifdef MINGW
 ifndef NOOPENMPT
 HAVE_OPENMPT=1
 endif
-else
-ifdef OPENMPT
-HAVE_OPENMPT=1
-endif
-endif
 
 ifdef MINGW
 include win32/Makefile.cfg