re PR tree-optimization/90671 (ICE on valid code at -Os and above with -g enabled in gsi_split_seq_after, at gimple-iterator.c:345)

	PR tree-optimization/90671
	* tree-ssa-threadupdate.c (ssa_create_duplicates): If
	template_block used to be empty on the first call, don't use
	gsi_split_seq_after and gsi_insert_seq_after, but remember whole
	seq with bb_seq and set it with set_bb_seq.

	* gcc.dg/torture/pr90671.c: New test.

From-SVN: r271802