Add compiler/system selections

[OneLoneCoder]

We need the usual top of file trickery for determining which audio driver to use

[viacheslavka]

I've taken care of it as part of my "make it build on linux" effort. I'll submit a PR later, if you don't mind

[OneLoneCoder]

Ok cool - theres a lot in the existing PGEX header too which maybe helpful

[viacheslavka]

I've taken care of it as part of my "make it build on linux" effort. I'll submit a PR later, if you don't mind.