Separate make-cont-folder into global and local variants

Separate make-cont-folder into global and local variants

* module/language/cps.scm (make-global-cont-folder)
  (make-local-cont-folder): Separate this macro in two.  It's hot and
  the difference can be important for perf.

* module/language/cps/dfg.scm (compute-label-and-var-ranges):
* module/language/cps/cse.scm (compute-label-and-var-ranges):
* module/language/cps/dce.scm (compute-live-code): Adapt.