mkrockspecs: set datarootdir instead of just datadir subset.
mkrockspecs: set datarootdir instead of just datadir subset.

* src/mkrockspecs.in (default.build): When using a GNU autotools
driven installation, set datarootdir so that (among others) the
documentation trees are installed to the correct rock directory.

Signed-off-by: Gary V. Vaughan <f9023000f29773649f3850298becb9544b5fd6a9@gnu.org>

gvvaughan/slingshot