Fortran: fix issues with variables in BLOCK DATA [PR58857]

Fortran: fix issues with variables in BLOCK DATA [PR58857]

	PR fortran/58857

gcc/fortran/ChangeLog:

	* class.cc (gfc_find_derived_vtab): Declare some frontend generated
	variables and procedures (_vtab, _copy, _deallocate) as artificial.
	(find_intrinsic_vtab): Likewise.
	* trans-decl.cc (check_block_data_decls): New helper function.
	(gfc_generate_block_data): Use it to emit warnings for variables
	declared in a BLOCK DATA program unit but not in a COMMON block.

gcc/testsuite/ChangeLog:

	* gfortran.dg/uncommon_block_data_2.f90: New test.