Essentially needed for packaging pulseaudio-modules-droid.

This package is basically a set of headers taken from
original pulseaudio tarball and one hand-made pkg-config file.

All versions listed in this package and in pulsecore.pc should
match pulseaudio's MAJOR.MINOR version, otherwise everything
will break. All library paths listed in pulsecore.pc should
match pulseaudio paths, too. Because library itself is built
and installed by pulseaudio package (pulseaudio-dev).

For motivation behind this see:
https://git.sailfishos.org/mer-core/pulseaudio/commit/9316d7ba941516cabfc080a0099fad80a231582d

TL;DR pulsecore is an internal pulseaudio library needed to build
pulseaudio's own modules, not meant to be used py pulseaudio clients.
It is not exported since pulseaudio-8. We fake an "export"
of this library, since we need it to build an out-of-tree module.