middle-end: refactor vectorizable_comparison to make the main body re-usable.

middle-end: refactor vectorizable_comparison to make the main body re-usable.

Vectorization of a gcond starts off essentially the same as vectorizing a
comparison witht he only difference being how the operands are extracted.

This refactors vectorable_comparison such that we now have a generic function
that can be used from vectorizable_early_break.  The refactoring splits the
gassign checks and actual validation/codegen off to a helper function.

No change in functionality expected.

gcc/ChangeLog:

	* tree-vect-stmts.cc (vectorizable_comparison): Refactor, splitting body
	to ...
	(vectorizable_comparison_1): ...This.