Start searching for headers and libraries under ${LOCALBASE}/ --
in case newer implementations of anything are installed there.

When compiling on 13.x or above, insist on libgnuregex version above
5 -- earlier FreeBSD releases came with libgnuregex.so.5, but that's
now gone and replaced by the devel/libgnuregex port, which currently
installs libgnuregex.so.6.

PR: 252252 252250 252245
Submitted by: kevans
Sponsored by: United Marsupials