[OpenACC 'exit data'] Evaluate 'finalize' individually for 'GOMP_MAP_STRUCT' entries

[OpenACC 'exit data'] Evaluate 'finalize' individually for 'GOMP_MAP_STRUCT' entries

Currently, we don't at all evaluate 'finalize' for 'GOMP_MAP_STRUCT' entries.
Fix this by copying/adapting the corresponding non-'GOMP_MAP_STRUCT' code.

	libgomp/
	* oacc-mem.c (goacc_exit_data_internal) <GOMP_MAP_STRUCT>:
	Evaluate 'finalize' individually for each entry.
	* testsuite/libgomp.oacc-c-c++-common/struct-1.c: New file.
	* testsuite/libgomp.oacc-c-c++-common/struct-refcount-1.c: Remove
	file.