Instead of installing them to /usr/libdata/pkgconfig, we use
/usr/lib<suffix>/pkgconfig. I'm not sure why native ABI libdirs are
installed to /usr/libdata/pkgconfig instead of /usr/lib/pkgconfig, but
I don't think this commit should change that.
This is a diff from CheriBSD, will update the review to use a FreeBSD baseline without the lib64 changes if this approach is acceptable.