* tree-ssa-threadupdate.c: Include tree-cfg.h and tree-pass.h
	(thread_block_1): Do not cancel jump threads which go from
	inside a loop, through the header, then back inside the loop.
	(bb_ends_with_multiway_branch): New function.
	(thread_through_all_blocks): Handle threading cases which start
	in a loop through the loop header to a point in the loop.

From-SVN: r205246