libgomp: Add interop types and routines to OpenMP's headers and module

This commit adds OpenMP 5.1+'s interop enumeration, type and routine
declarations to the C/C++ header file and, new in OpenMP TR13, also to
the Fortran module and omp_lib.h header file.

While a stub implementation is provided, only with foreign runtime
support by the libgomp GPU plugins and with the 'interop' directive,
this becomes really useful.

libgomp/ChangeLog:

	* fortran.c (omp_get_interop_str_, omp_get_interop_name_,
	omp_get_interop_type_desc_, omp_get_interop_rc_desc_): Add.
	* libgomp.map (GOMP_5.1.3): New; add interop routines.
	* omp.h.in: Add interop typedefs, enum and prototypes.
	(__GOMP_DEFAULT_NULL): Define.
	(omp_target_memcpy_async, omp_target_memcpy_rect_async):
	Use it for the optional depend argument.
	* omp_lib.f90.in: Add paramters and interfaces for interop.
	* omp_lib.h.in: Likewise; move F90 '&' to column 81 for
	-ffree-length-80.
	* target.c (omp_get_num_interop_properties, omp_get_interop_int,
	omp_get_interop_ptr, omp_get_interop_str, omp_get_interop_name,
	omp_get_interop_type_desc, omp_get_interop_rc_desc): Add.
	* config/gcn/target.c (omp_get_num_interop_properties,
	omp_get_interop_int, omp_get_interop_ptr, omp_get_interop_str,
	omp_get_interop_name, omp_get_interop_type_desc,
	omp_get_interop_rc_desc): Add.
	* config/nvptx/target.c (omp_get_num_interop_properties,
	omp_get_interop_int, omp_get_interop_ptr, omp_get_interop_str,
	omp_get_interop_name, omp_get_interop_type_desc,
	omp_get_interop_rc_desc): Add.
	* testsuite/libgomp.c-c++-common/interop-routines-1.c: New test.
	* testsuite/libgomp.c-c++-common/interop-routines-2.c: New test.
	* testsuite/libgomp.fortran/interop-routines-1.F90: New test.
	* testsuite/libgomp.fortran/interop-routines-2.F90: New test.
	* testsuite/libgomp.fortran/interop-routines-3.F: New test.
	* testsuite/libgomp.fortran/interop-routines-4.F: New test.
	* testsuite/libgomp.fortran/interop-routines-5.F: New test.
	* testsuite/libgomp.fortran/interop-routines-6.F: New test.
	* testsuite/libgomp.fortran/interop-routines-7.F90: New test.