[pcm] fix default install paths for mac os
[pcm] fix default install paths for mac os

Since El Capitan /usr/lib & /usr/include are not writable even for root: https://support.apple.com/en-us/HT204899,
thus, running `make install` fails.

/usr/local/lib still is writable, and seems like a better option for a
default install script.

Test plan:
1) make uninstall old version, for which i copied files manually;
2) make install for new version
3) build pcm.x
4) run it, confirm it works.

opcm/pcm,opcm/pcm,opcm/pcm,opcm/pcm