Implement OpenMP 5.1 section 3.15: omp_display_env

This is a new interface which is easily implemented using the
already existing code for the handling of the OMP_DISPLAY_ENV
environment variable.

libgomp/
	* env.c (wait_policy, stacksize): New static variables,
	move out of handle_omp_display_env.
	(omp_display_env): New function.  The meat of the old
	handle_omp_display_env function.
	(handle_omp_display_env): Change to not take parameters
	and instead use the global variables.  Only perform
	parsing, defer to omp_display_env for the implementation.
	(initialize_env): Remove local variables wait_policy and
	stacksize.  Don't pass parameters to handle_omp_display_env.
	* fortran.c: Add ialias_redirect for omp_display_env.
	(omp_display_env_, omp_display_env_8_): New functions.
	* libgomp.map (OMP_5.1): New version.  Add omp_display_env,
	omp_display_env_, and omp_display_env_8_.
	* omp.h.in: Declare omp_display_env.
	* omp_lib.f90.in: Likewise.
	* omp_lib.h.in: Likewise.