Prevent malicious descriptor stacking for scalar components [V2].

Prevent malicious descriptor stacking for scalar components [V2].

gcc/fortran/ChangeLog:

	PR fortran/103790
	* trans-array.cc (structure_alloc_comps): Prevent descriptor
	stacking for non-array data; do not broadcast caf-tokens.
	* trans-intrinsic.cc (conv_co_collective): Prevent generation
	of unused descriptor.

gcc/testsuite/ChangeLog:

	PR fortran/103790
	* gfortran.dg/coarray_collectives_18.f90: New test.