rtld only needs shared objects, so the other patterns are pointless and
significantly increase the work make has to perform while identifying
which pattern rule to apply.
The third arg can either be a string with "g" or "G", or it is a number.
The empty string elicits a warning with newer versions like so:
gawk: scripts/sysd-rules.awk:56: warning: gensub: third argument `' treated as 1
Florian Weimer
Nick Alcock
Mike Frysinger
Roland McGrath