re PR lto/65515 (FAIL: gcc.c-torture/compile/limits-fndefn.c   -O2 -flto -flto-partition=none  (ICE) -- SIGSEGV for stack growth failure)

	PR lto/65515
	* lto-streamer-out.c (DFS::worklist): New struct.
	(DFS::worklist_vec): New data member.
	(DFS::next_dfs_num): Remove.
	(DFS::DFS): Rewritten using worklist instead of recursion,
	using most of code from DFS::DFS_write_tree.
	(DFS::DFS_write_tree_body): Remove SINGLE_P argument, don't
	pass it to DFS_write_tree calls.
	(DFS::DFS_write_tree): Remove SINGLE_P argument, after
	quick initial checks push it into worklist_vec and return.

From-SVN: r221656