Fix some memory leaks

Fix some memory leaks

The following fixes memory leaks found compiling SPEC CPU 2017 with
valgrind.

	* df-core.cc (rest_of_handle_df_finish): Release dflow for
	problems without free function (like LR).
	* gimple-crc-optimization.cc (crc_optimization::loop_may_calculate_crc):
	Release loop_bbs on all exits.
	* tree-vectorizer.h (supportable_indirect_convert_operation): Change.
	* tree-vect-generic.cc (expand_vector_conversion): Adjust.
	* tree-vect-stmts.cc (vectorizable_conversion): Use auto_vec for
	converts.
	(supportable_indirect_convert_operation): Get a reference to
	the output vector of converts.