squash! mescc: Fix switch statements' fallthrough

This reverts commit ef4f4bb25a.

module/mescc/compile.scm

@@ -1791,29 +1791,27 @@
                  (set! i (1+ i)))
                n))))
 
-        (define (flatten-cases c)
-          (define (flatten-case case)
-            (pmatch case
-              ((case ,test (case . ,body))
-               (append `((case ,test (expr-stmt))) (flatten-case `(case ,@body))))
-              ((case ,test ,casebody (case . ,body))
-               (append `((case ,test ,casebody)) (flatten-case `(case ,@body))))
-              ((default (case . ,body))
-               (append `((default (expr-stmt))) (flatten-case `(case ,@body))))
-              ((default ,defbody (case . ,body))
-               (append `((default ,defbody)) (flatten-case `(case ,@body))))
-              ((case ,test (default . ,body))
-               (append `((case ,test (expr-stmt))) (flatten-case `(default ,@body))))
-              ((default ,rest)
-               (list case))
-              ((case ,test)
-               (list case))
-              ((case ,test ,expr)
-               (list case))
-              (,s (list s))))
-          (fold (lambda (x acc) (append acc (flatten-case x))) '() c))
-
-
+       (define (flatten-cases c)
+         (define (flatten-case o)
+           (pmatch o
+             ((case ,test (case . ,body))
+              (cons `(case ,test (expr-stmt)) (flatten-case `(case ,@body))))
+             ((case ,test ,case-body (case . ,body))
+              (cons `(case ,test ,case-body) (flatten-case `(case ,@body))))
+             ((default (case . ,body))
+              (cons `(default (expr-stmt)) (flatten-case `(case ,@body))))
+             ((default ,default-body (case . ,body))
+              (cons `(default ,default-body) (flatten-case `(case ,@body))))
+             ((case ,test (default . ,body))
+              (cons `(case ,test (expr-stmt)) (flatten-case `(default ,@body))))
+             ((default ,rest)
+              (list o))
+             ((case ,test)
+              (list o))
+             ((case ,test ,expr)
+              (list o))
+             (,s (list s))))
+         (fold (lambda (x acc) (append acc (flatten-case x))) '() c))
 
        (let* ((info (append-text info (ast->comment `(switch ,expr (compd-stmt (block-item-list (ellipsis)))))))
               (statements (flatten-cases statements))