Not loading two lib at same time

[Darknior]

Add IF to not load the two lib at same time and crash the MAKE.
Use XMP in first because it give the best sound support with music LOOP.

[carstene1ns]

Not too happy with this situation, the build failure should be solved, yes.
However, I would like to leave ModPlug as default library, partly because of the good license.
(Also it sounds better than xmp to me, i.e. richer sound)

In the future I plan to support even more music libraries: OpenMPT and DUMB. Then this situation gets even worse. For the time being I think some boolean algebra in sound.cpp will suffice.

[Darknior]

Like you want, on PI (linux) XMP is better. I think the sound is richer like Modplug because i try the two lib and don't see any difference. Only that Modplug don't loop.