Revert "Search in default path before calling pkg-config"
Build system changes can be potentially breaking and so must be reviewed
prior to commit. In addition, there is no explanation for this change.
Simon, you might want to submit your patches to Phabricator for review
prior to landing them.
CCMAIL: sdepiets@gmail.com
This reverts commit d9578de8298f75f3c65c55ec8621cdb1a925c092.