enhance conditionals (#2966)

- `x ? (y, w) : (z, w)` => `x ? y : z, w`

test/compress/conditionals.js

@@ -332,7 +332,7 @@ cond_7: {
         x = 'foo';
         x = 'foo';
         x = (condition(), 20);
-        x = z ? 'fuji' : (condition(), 'fuji');
+        x = (z || condition(), 'fuji');
         x = (condition(), 'foobar');
         x = y ? a : b;
         x = y ? 'foo' : 'fo';

test/compress/transform.js

@@ -104,6 +104,7 @@ if_return: {
         conditionals: true,
         if_return: true,
         sequences: true,
+        side_effects: true,
     }
     input: {
         function f(w, x, y, z) {
@@ -124,7 +125,7 @@ if_return: {
                 if (w) {
                     if (y) return;
                 } else if (z) return;
-                return x == y || (x && w(), y && z(), !0);
+                return x == y || (x && w(), y && z()), !0;
             }
         }
     }