re PR lto/50430 (Constructors of static external vars are throwed away leading to missed optimizations (and ipa-cp ICE).)

	PR lto/50430
	* gimple-fold.c (gimple_get_virt_method_for_binfo): Do not ICE on
	error_mark_node in the DECL_INITIAL of vtable.

From-SVN: r178908