re PR c++/70615 (ICE on valid code at -O1 and above on x86_64-linux-gnu in add_expr, at tree.c:7870)

	PR c++/70615
	* cp-gimplify.c (cp_genericize_r): Expand PTRMEM_CST here.
	(cp_gimplify_expr): Not here.

From-SVN: r234940