...by including `vecLib/vecLib.h` only on `__APPLE__`, and not just any `__ppc__`
From https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=235668:
> On powerpc* platforms vecLib/vecLib.h is included by default.
> This header is only available on Mac OS X, so remove it. It
> doesn't seem to be actually needed to compile this port.
Don't include the lazy precompiled.h everywhere, only what's
required for the compilation unit.
platform.h needs to be included instead to provide all essential
defines and types.
All includes use the relative path to the neo or the game
specific root.
Move all idlib related includes from idlib/Lib.h to precompiled.h.
precompiled.h still exists for the MFC stuff in tools/.
Add some missing header guards.
