Fix failures with -m32 and some memory leaks.

Fix failures with -m32 and some memory leaks.

2020-12-23  Paul Thomas  <pault@gcc.gnu.org>

gcc/fortran
	PR fortran/83118
	* trans-array.c (gfc_alloc_allocatable_for_assignment): Make
	sure that class expressions are captured for dummy arguments by
	use of gfc_get_class_from_gfc_expr otherwise the wrong vptr is
	used.
	* trans-expr.c (gfc_get_class_from_gfc_expr): New function.
	(gfc_get_class_from_expr): If a constant expression is
	encountered, return NULL_TREE;
	(gfc_trans_assignment_1): Deallocate rhs allocatable components
	after passing derived type function results to class lhs.
	* trans.h : Add prototype for gfc_get_class_from_gfc_expr.