Teach OpenMP Library to use Hwloc on Windows

This patch allows a user to enable Hwloc on windows. There are three main
changes in here:
1.kmp.h - Move definitions/declarations out of KMP_OS_WINDOWS guard (our windows
          implementation of affinity) because they need to be defined when
          KMP_USE_HWLOC is on as well.
2.teach __kmp_set_system_affinity, __kmp_get_system_affinity,
        __kmp_get_proc_group, and __kmp_affinity_bind_thread how to use hwloc.
3.teach CMake how to include hwloc when building Windows

Another minor change in here is to make sure that anything under KMP_USE_HWLOC
is also guarded by KMP_AFFINITY_SUPPORTED as well. This is to prevent Mac
builds from requiring anything from Hwloc.

Differential Revision: http://reviews.llvm.org/D21441

llvm-svn: 272951