get sysimg building with new binding behavior (ref #1571)

the most problematic change was forcing for loop variables to be loop-local,
instead of reusing existing local vars. for example

    local i
    for i = 1:2
    end
    return i

currently works and returns 2.

for now, the behavior is to introduce new variables for each iteration unless
we are overwriting an existing local. comprehensions, however, always
introduce fresh variables and never overwrite existing ones.

src/julia-syntax.scm

@@ -1440,7 +1440,8 @@
 			(_while (call (top <=) ,cnt ,lim)
 				(scope-block
 				 (block
-				  (local ,lhs)
+				  ;; NOTE: enable this to force loop-local var
+				  #;(local ,lhs)
 				  (= ,lhs ,cnt)
 				  (break-block loop-cont
 					       ,body)
@@ -1459,7 +1460,8 @@
 	       (while (call (top !) (call (top done) ,coll ,state))
 		      (scope-block
 		       (block
-			,@(map (lambda (v) `(local ,v)) (lhs-vars lhs))
+			;; NOTE: enable this to force loop-local var
+			#;,@(map (lambda (v) `(local ,v)) (lhs-vars lhs))
 			,(lower-tuple-assignment (list lhs state)
 						 `(call (top next) ,coll ,state))
 			,body)))))))
@@ -1660,7 +1662,11 @@
 		    (boundscheck pop)
 		    (= ,ri (call (top +) ,ri 1)))
 	    `(for (= ,(cadr (car ranges)) ,(car rs))
-		  ,(construct-loops (cdr ranges) (cdr rs)))))
+		  (block
+		   ;; *** either this or force all for loop vars local
+		   ,@(map (lambda (r) `(local ,r))
+			  (lhs-vars (cadr (car ranges))))
+		   ,(construct-loops (cdr ranges) (cdr rs))))))
 
       ;; Evaluate the comprehension
       `(block
@@ -1694,7 +1700,11 @@
 		    (type_goto ,initlabl ,onekey ,oneval)
 		    (call (top setindex!) ,result ,oneval ,onekey))
 	    `(for ,(car ranges)
-		  ,(construct-loops (cdr ranges)))))
+		  (block
+		   ;; *** either this or force all for loop vars local
+		   ,@(map (lambda (r) `(local ,r))
+			  (lhs-vars (cadr (car ranges))))
+		   ,(construct-loops (cdr ranges))))))
 
       ;; Evaluate the comprehension
       (let ((loopranges
@@ -1730,7 +1740,11 @@
 	(if (null? ranges)
 	    `(call (top setindex!) ,result ,(caddr expr) ,(cadr expr))
 	    `(for (= ,(cadr (car ranges)) ,(car rs))
-		  ,(construct-loops (cdr ranges) (cdr rs)))))
+		  (block
+		   ;; *** either this or force all for loop vars local
+		   ,@(map (lambda (r) `(local ,r))
+			  (lhs-vars (cadr (car ranges))))
+		   ,(construct-loops (cdr ranges) (cdr rs))))))
 
       ;; Evaluate the comprehension
       `(block
@@ -2208,7 +2222,7 @@ So far only the second case can actually occur.
 		    (body (add-local-decls (cadr e) (append vars glob env))))
 	       `(scope-block ,@(map (lambda (v) `(local ,v))
 				    vars)
-			     ,(prn (remove-local-decls (prn body))))))
+			     ,(remove-local-decls body))))
 	    (else
 	     ;; form (local! x) adds a local to a normal (non-scope) block
 	     (let ((newenv (append (declared-local!-vars e) env)))