Fix initialization of UNIONs with -finit-derived.

Fix initialization of UNIONs with -finit-derived.

	gcc/fortran/
	* expr.c (generate_union_initializer, get_union_initializer): New.
	* expr.c (component_initializer): Consider BT_UNION specially.
	* resolve.c (resolve_structure_cons): Hack for BT_UNION.
	* trans-expr.c (gfc_trans_subcomponent_assign): Ditto.
	* trans-expr.c (gfc_conv_union_initializer): New.
	* trans-expr.c (gfc_conv_structure): Replace UNION handling code with
	new function gfc_conv_union_initializer.

	gcc/testsuite/gfortran.dg/
	* dec_init_1.f90, dec_init_2.f90: Remove -fdump-tree-original.
	* dec_init_3.f90, dec_init_4.f90: New tests.

From-SVN: r241626