get platformX86UNIX compiling.

Almost certainly broken.  Got the GL API binding stuff working by
simply removing it; we probably have null function pointers now,
but I think almost all this code can be replaced with GLEW anyway.

OpenAL might also be broken similarly.  We can probably just drop
the indirection here.
Don't build with fmod on Linux.

Temporarily?  Big can of worms, not easy to install.
Linux: add simple missing libraries to build.

"simple" meaning they exist as part of package managers and can
just be installed on the host system.  Maybe the other libraries
exist in the source tree somewhere, and could be used from there.
Simplify typing considerably.

Use only the types from platform/types.h, which are now
cross-platform/compiler.
Remove unused typedef/ifdef.