* Allow for adding constraints targetting blocks with multiple predecessors

* Allow for adding constraints targetting blocks with multiple predecessors

This commit remove the limitaiton we had not being able to add
constraints derived from conditional branches to basic blocks with
multiple predecessors.  When this condition is verified we add a new
dedicated basic block to hold the constraints.

	* lisp/emacs-lisp/comp.el (comp-block, comp-edge): Better slot
	type specifiers.
	(comp-block-cstr): New struct specializing `comp-block'.
	(make-comp-edge): New function.
	(comp-func): Better test function + doc for `blocks' slot.
	(comp-limple-lock-keywords): Update possible basic block names.
	(comp-emit-assume): Recive directly the block instead of its name.
	(comp-add-new-block-beetween): New function.
	(comp-cond-cstr-target-block): Logic update and use
	`comp-add-new-block-beetween'.
	(comp-cond-cstr-func): Make use of the latter.
	(comp-compute-edges): Make use of `make-comp-edge'.