[arch-dev-public] Replacing pkg-config with pkgconf

[Jan Alexander Steffens]

I want to replace pkg-config with pkgconf, an implementation that's
actively maintained.

https://github.com/pkgconf/pkgconf/

pkgconf is reportedly both faster and has saner behavior.

For example, right now `pkg-config --exists OpenEXR` fails if glu is not
installed, since OpenEXR has a "private" dependency on glu.
However, `pkg-config --libs OpenEXR` works since pkg-config ignores private
dependencies here.

Private dependencies are relevant for static linking, analogous to a shared
library's DT_NEEDED tags.
`pkg-config --static --libs OpenEXR` lists the libraries necessary to
statically link OpenEXR.

pkgconf is more consistent and follows private dependencies only if
--static is given, regardless of whether --libs or --exists is used.

pkgconf is in use by at least FreeBSD, NetBSD, Fedora and Mageia; so we
wouldn't be the first ones making the switch.

There's already a package in [community] owned by demize. I would make some
adjustments before releasing it to [testing].

Any objections?