Use system installed libportaudio.a on Linux if present

[musger]

Would it be possible to use a system-wide installed libportaudio.a for compilation on Linux if this file is present? Ths would remove the need to compile the version included with CDP.

[musger]

I have to correct myself. It seems that currently a system-wide installed libportaudio.a is found by cmake by default on Debian/GNU Linux in /usr/lib/x86_64-linux-gnu/libportaudio.a after installing the libportaudio-dev package.

Does the cmake cache entry USE_LOCAL_PORTAUDIO enable or disable building programs that depend on portaudio or does it control which libportaudio.a is used for compilation? Is the version distributed with the sources here in dev/externals/paprogs/portaudio used by default, used at all, or only used on windows?