xbps-src: follow symlinks when fixing up pkg-config files

Packages (e.g., python3-pybind11) that symlink to *.pc files in
/usr/{lib,share}/pkgconfig will have those links overwritten with actual
copies of the files after the hook

    common/hooks/post-install/13-pkg-config-clean-xbps-cross-base-ref.sh

attempts to remove $XBPS_CROSS_BASE from paths. This will result in the
new copy containing corrected paths, but the original file remaining
uncorrected.

This was stolen fro @tornaria.

common/hooks/post-install/13-pkg-config-clean-xbps-cross-base-ref.sh

@@ -16,7 +16,8 @@ hook() {
 			# s,/usr/armv7l-linux-musleabihf/usr,/usr,g
 			# trailing /usr to avoid clashing with
 			# other $XBPS_CROSS_BASE and $XBPS_CROSS_TRIPLET.
-			sed -i -e "s,$XBPS_CROSS_BASE/usr,/usr,g" "$f"
+			sed -i --follow-symlinks \
+				-e "s,$XBPS_CROSS_BASE/usr,/usr,g" "$f"
 		fi
 	done
 }