Not only is FMOD neither free (libre) nor free (gratis), the version we
support(ed) is also impossible to legally obtain anymore. So there's no
reason we should keep code around that (pretends to) support a library
nobody can use or test.
OpenAL's pkg-config database doesn't list include/AL as a location for
AL headers, but including <AL/al.h> is unusable because some systems
store the headers in OpenAL instead of AL. So check if the file can
actually be found as <al.h> and amend the include directory list
otherwise.
There's no point in splitting the audio library selection into multiple
CPP macros, since there can always only be one anyway. Merge all of them
into a single macro AUDIO_TK (for "toolkit") and have CMake select one
for the user, instead of making him choose (and potentially failing).
Nicolas Hake