Previously, findstring matched on amazonlinux2 too, breaking the build on that OS.

Previously, we required an exact non-virtual package, however it's fine
if some package has a fully-virtual provides for what we need.

In BSD systems, it's usually </var/db> or some other dir under </var>
that is not </var/lib>, so $statedir is a more generic name.  See
hier(7).

Reported-by: Andrei Zeliankou <zelenkov@nginx.com>
Reported-by: Zhidao Hong <z.hong@f5.com>
Reviewed-by: Konstantin Pavlov <thresh@nginx.com>
Reviewed-by: Andrew Clayton <a.clayton@nginx.com>
Cc: Liam Crilly <liam@nginx.com>
Signed-off-by: Alejandro Colomar <alx@nginx.com>

These directories are used in the Makefile to determine status of a target.

pkg-config package is named differently on supported rpm-based systems:
- Amazon Linux 2 has pkgconfig
- Fedora has pkgconf-pkg-config
- RHEL 7 has pkgconfig
- RHEL 8 and 9 have pkgconfig-pkg-config

What they share in common is they all provide 'pkgconfig', which we can
use in the spec file so we don't have to specify it per-OS.