PKG_CONFIG_PATH incorrect for multiarch on Debian

Submitted by Richard Webb

Description

It seems that the PKG_CONFIG_PATH that is set up in cerbero/utils/__init__.py is not always correct.

On the board I am currently using (Wandboard with Ubuntu 14.04) for instance, arch specific pkgconfigs are in /usr/lib/arm-linux-gnueabihf/pkgconfig, while the python script assumes this is always 'usr/lib/%s-linux-gnu/pkgconfig' % arch. This doesn't take into account the Multiarch tuples as specified here:

https://wiki.debian.org/Multiarch/Tuples

I would suggest that this is changed (on Debian) to include the output of the following command:

dpkg-architecture -qDEB_HOST_MULTIARCH

On my system, the above outputs the correct multiarch tuple: arm-linux-gnueabihf.

Happy to attempt a patch if this seems acceptable.