taskd: add patch for correct gnutls libraries in static build

taskd: add patch for correct gnutls libraries in static build

The CMakeLists.txt was using the wrong variables names to add to
includes and libs, so the additional libraries for static build
weren't added to the link command.

Patch sent upstream to taskwarrior-dev@googlegroups.com but it doesn't
seem to be very active.

Fixes:
http://autobuild.buildroot.net/results/d01e947fa807336ffcfd0fad27397af8e7442833

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>