Enable via yul or explain why disabled.

test/libsolidity/semanticTests/modifiers/function_modifier_loop.sol

@@ -8,6 +8,11 @@ contract C {
         r += 1;
     }
 }
+// via yul disabled because the return variables are
+// fresh variables each time, while in the old code generator,
+// they share a stack slot when the function is
+// invoked multiple times via `_`.
+
 // ====
 // compileViaYul: false
 // ----