sparse: update to support llvm 3.5.0

sparse-0.5.0 won't link against lvm 3.5.0 as "llvm-config --libs" does not
include system libs like pthreads. This problem got fixed but not released
yet, so we need to fetch from their git repo.

Signed-off-by: Stefan Sydow <stefan.sydow@tu-berlin.de>