Fix Intel MIC 'mkoffload' for OpenMP 'requires'

Fix Intel MIC 'mkoffload' for OpenMP 'requires'

Similar to how the other 'mkoffload's got changed in
recent commit 683f11843974f0bdf42f79cdcbb0c2b43c7b81b0
"OpenMP: Move omp requires checks to libgomp".

This also means finally switching Intel MIC 'mkoffload' to
'GOMP_offload_register_ver', 'GOMP_offload_unregister_ver',
making 'GOMP_offload_register', 'GOMP_offload_unregister'
legacy entry points.

	gcc/
	* config/i386/intelmic-mkoffload.cc (generate_host_descr_file)
	(prepare_target_image, main): Handle OpenMP 'requires'.
	(generate_host_descr_file): Switch to 'GOMP_offload_register_ver',
	'GOMP_offload_unregister_ver'.
	libgomp/
	* target.c (GOMP_offload_register, GOMP_offload_unregister):
	Denote as legacy entry points.
	* testsuite/lib/libgomp.exp
	(check_effective_target_offload_target_any): New proc.
	* testsuite/libgomp.c-c++-common/requires-1.c: Enable for
	'offload_target_any'.
	* testsuite/libgomp.c-c++-common/requires-3.c: Likewise.
	* testsuite/libgomp.c-c++-common/requires-7.c: Likewise.
	* testsuite/libgomp.fortran/requires-1.f90: Likewise.