compiler.cfg: move back-edge? word from stack-analysis to top-level vocab

basis/compiler/cfg/cfg.factor

@@ -48,6 +48,9 @@ SYMBOL: visited
         building get push
     ] with-variable ; inline
 
+: back-edge? ( from to -- ? )
+    [ number>> ] bi@ > ;
+
 TUPLE: cfg { entry basic-block } word label spill-counts post-order ;
 
 : <cfg> ( entry word label -- cfg ) f f cfg boa ;

basis/compiler/cfg/stack-analysis/stack-analysis.factor

@@ -60,9 +60,6 @@ UNION: sync-if-back-edge
     ##dispatch
     ##loop-entry ;
 
-: back-edge? ( from to -- ? )
-    [ number>> ] bi@ > ;
-
 : sync-state? ( -- ? )
     basic-block get successors>>
     [ [ predecessors>> ] keep '[ _ back-edge? ] any? ] any? ;