openmp: Handle OpenMP 5.1 simplified OMP_PLACES syntax

openmp: Handle OpenMP 5.1 simplified OMP_PLACES syntax

In addition to adding ll_caches and numa_domain abstract names
to OMP_PLACES syntax, OpenMP 5.1 also added one syntax simplification:
https://github.com/OpenMP/spec/issues/2080
https://github.com/OpenMP/spec/pull/2081
in particular that in the grammar place non-terminal is now
not only { res-list } but also res (i.e. a non-negative integer),
which stands as a shortcut for { res }
So, one can specify OMP_PLACES=0,4,8,12 with the meaning
OMP_PLACES={0},{4},{8},{12} or OMP_PLACES=0:4 instead of OMP_PLACES={0}:4
or OMP_PLACES={0},{1},{2},{3} etc.

This patch implements that.

2021-10-15  Jakub Jelinek  <jakub@redhat.com>

	* env.c (parse_one_place): Handle non-negative-number the same
	as { non-negative-number }.  Reject even !number:1 and
	!number:1:stride or !place:1 or !place:1:stride instead of just
	length other than 1.
	* libgomp.texi (OpenMP 5.1): Document OMP_PLACES syntax extensions
	and OMP_NUM_TEAMS/OMP_TEAMS_THREAD_LIMIT and
	omp_{set_num,get_max}_teams/omp_{s,g}et_teams_thread_limit features
	as implemented.
	* testsuite/libgomp.c/affinity-1.c: Add a test for the 5.1 place
	simplified syntax.