Add new OpenMP 4.5 affinity API

This change introduces the new OpenMP 4.5 affinity api surrounding
OpenMP Places. There are six new entry points:

Typically called in serial region:
 * omp_get_num_places - returns the number of places available to the execution
       environment in the place list.
 * omp_get_place_num_procs - returns the number of processors available to the
       execution environment in the specified place.
 * omp_get_place_proc_ids - returns the numerical identifiers of the processors
       available to the execution environment in the specified place.

Typically called inside parallel region:
 * omp_get_place_num - returns the place number of the place to which the
       encountering thread is bound.
 * omp_get_partition_num_places - returns the number of places in the place
       partition of the innermost implicit task.
 * omp_get_partition_place_nums - returns the list of place numbers
       corresponding to the places in the place-var ICV of the innermost
       implicit task.

Differential Revision: http://reviews.llvm.org/D17417

llvm-svn: 261915