depends: fix Boost 1.55 build on GCC 5

Boost assumes variadic templates are always available in GCC 4.4+, but
they aren't since we don't build with -std=c++11.

This applies the patch that fixed the issue in boost 1.57:
https://github.com/boostorg/config/commit/eec808554936ae068b23df07ab54d4dc6302a695

See also: https://svn.boost.org/trac/boost/ticket/10500