wildmidi.c: made several vars and funcs static, removed unused ones.
gus_pat.c: made the convert_* funcs static.
wildmidi_lib.c: made the vars patch[], reverb_room_*, reverb_listen_*,
fix_release, auto_amp*, and the funcs load_sample and get_decay_samples
static.
wildmidi_lib.c: don't call exit() from the library. clean that part a bit, as well.
cmake: clean up visibility attributes and move them to wildmidi_dynamic
target only. add an untested support for sunpro compiler.  adjusted the
wildmidi_lib.h header for the changes.