This was a little messy to implement, as (a) libinih-dev does not have the same package name on all platforms, and (b) PCP builds for some platforms where there is no vendor-supplied package to deliver <ini.h> and libinih.so.
However this work is now done and PCP will use the vendor-supplied package if configure detects the required files are installed, else fallback to the source version in the PCP tree (which we're easily able to refresh from https://github.com/benhoyt/inih as required). Commits https://github.com/performancecopilot/pcp/commit/e398f288e161eab6b5b43a87044313dce2a46d77 and https://github.com/performancecopilot/pcp/commit/df7f5523c7db665caff5949597a31bf5c33b764b provide the required fixes in the upstream PCP tree.
