add move CTOR to auto_vec, use auto_vec for get_loop_exit_edges

add move CTOR to auto_vec, use auto_vec for get_loop_exit_edges

This adds a move CTOR to auto_vec<T, 0> and makes use of a
auto_vec<edge> return value for get_loop_exit_edges denoting
that lifetime management of the vector is handed to the caller.

The move CTOR prompted the hash_table change because it appearantly
makes the copy CTOR implicitely deleted (good) and hash-table
expansion of the odr_enum_map which is
hash_map <nofree_string_hash, odr_enum> where odr_enum has an
auto_vec<odr_enum_val, 0> member triggers this.  Not sure if
there's a latent bug there before this (I think we're not
invoking DTORs, but we're invoking copy-CTORs).

2020-08-06  Richard Biener  <rguenther@suse.de>

	* vec.h (auto_vec<T, 0>::auto_vec (auto_vec &&)): New move CTOR.
	(auto_vec<T, 0>::operator=(auto_vec &&)): Delete.
	* hash-table.h (hash_table::expand): Use std::move when expanding.
	* cfgloop.h (get_loop_exit_edges): Return auto_vec<edge>.
	* cfgloop.c (get_loop_exit_edges): Adjust.
	* cfgloopmanip.c (fix_loop_placement): Likewise.
	* ipa-fnsummary.c (analyze_function_body): Likewise.
	* ira-build.c (create_loop_tree_nodes): Likewise.
	(create_loop_tree_node_allocnos): Likewise.
	(loop_with_complex_edge_p): Likewise.
	* ira-color.c (ira_loop_edge_freq): Likewise.
	* loop-unroll.c (analyze_insns_in_loop): Likewise.
	* predict.c (predict_loops): Likewise.
	* tree-predcom.c (last_always_executed_block): Likewise.
	* tree-ssa-loop-ch.c (ch_base::copy_headers): Likewise.
	* tree-ssa-loop-im.c (store_motion_loop): Likewise.
	* tree-ssa-loop-ivcanon.c (loop_edge_to_cancel): Likewise.
	(canonicalize_loop_induction_variables): Likewise.
	* tree-ssa-loop-manip.c (get_loops_exits): Likewise.
	* tree-ssa-loop-niter.c (find_loop_niter): Likewise.
	(finite_loop_p): Likewise.
	(find_loop_niter_by_eval): Likewise.
	(estimate_numbers_of_iterations): Likewise.
	* tree-ssa-loop-prefetch.c (emit_mfence_after_loop): Likewise.
	(may_use_storent_in_loop_p): Likewise.