ARM Limited license agreement from the copyright/patent holder

I have prepared some patches for LLVM OpenMP runtime, mostly addressing
ARMv8 support. Before I upstream them, I must address legal issues that
arose around my planned contribution. I was advised that before I send any
substantial commit, I need to make sure that LICENSE.txt file in the projects
repository contains a statement submitted by ARM, similar to the one provided
by Intel (see "a license agreement from the copyright/patent holders"). This is
the same situation as with top-level LLVM project: ARM has provided the same
statement in http://llvm.org/svn/llvm-project/llvm/trunk/lib/Target/ARM/LICENSE.TXT file.

Patch by Paul Osmialowski

Differential Revision: http://reviews.llvm.org/D19319