PR libgomp/42942
	* env.c (parse_unsigned_long): Add ALLOW_ZERO argument.
	(initialize_env): Adjust callers.
	(omp_set_max_active_levels): Set gomp_max_active_levels_var even
	when the argument is 0.

	* testsuite/libgomp.c/pr42942.c: New test.

From-SVN: r157635