Update devel/llbuild to SNAPSHOT-2017-12-10.

This update simplifies the build, as upstream has incorporated many of the
patches that used to be in the files directory of this port. It also
updates the distinfo to fix the previous BROKEN line.

Approved by: mat
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D13451