[Patch (preapproved)] Guard Copy Header pass on

[Patch (preapproved)] Guard Copy Header pass on

While answering a user question on the equivalence of
-ftree-loop-vectorize + -ftree-slp-vectorize and -ftree-vectorize I
spotted one case which broke the equivalence. pass_ch::process_loop_p
was guarded on flag_tree_vectorize, meaning you would get it for
-ftree-vectorize, but not for -ftree-loop-vectorize/-ftree-slp-vectorize.

This patch fixes that, getting rid of the only use of flag_tree_vectorize
in the code base.

gcc/

	* tree-ssa-loop-ch.c (pass_ch::process_loop_p): Guard on
	flag_tree_loop_vectorize rather than flag_tree_vectorize.

From-SVN: r250619