This patch fixes PR97045 - unlimited polymorphic array element selectors.

This patch fixes PR97045 - unlimited polymorphic array element selectors.

2020-30-09  Paul Thomas  <pault@gcc.gnu.org>

gcc/fortran
	PR fortran/97045
	* trans-array.c (gfc_conv_array_ref): Make sure that the class
	decl is passed to build_array_ref in the case of unlimited
	polymorphic entities.
	* trans-expr.c (gfc_conv_derived_to_class): Ensure that array
	refs do not preceed the _len component. Free the _len expr.
	* trans-stmt.c (trans_associate_var): Reset 'need_len_assign'
	for polymorphic scalars.
	* trans.c (gfc_build_array_ref): When the vptr size is used for
	span, multiply by the _len field of unlimited polymorphic
	entities, when non-zero.

gcc/testsuite/
	PR fortran/97045
	* gfortran.dg/select_type_50.f90 : New test.