loki ~ # equery files x11-themes/gnome-icon-theme-2.24.0|grep '\.pc' /usr/share/pkgconfig/gnome-icon-theme.pc
You're going to have to argue on what is wrong with this... see comment #1 of bug #244840
From how I read the man page, it seemed that /usr/shar/pkgconfig wouldn't be searched: pkg-config retrieves information about packages from special metadata files. These files are named after the package, with the extension .pc. By default, pkg-config looks in the directory prefix/lib/pkgconfig for these files; it will also look in the colon-separated (on Windows, semi‐ colon-separated) list of directories specified by the PKG_CONFIG_PATH environment variable. I just now read further down where that is contradicted: A colon-separated (on Windows, semicolon-separated) list of directories to search for .pc files. The default directory will always be searched after searching the path; the default is libdir/pkgconfig:datadir/pkgconfig where libdir is the libdir where pkg-config and datadir is the datadir where pkg-config was installed. Closing as invalid then.
pkg-config upstream has a long outstanding manual bug with patches to still resolve. Upstream maintainer is AWOL
I mean manual page patch to make it match reality in regards to default search path.