clean up negate_iife

- remove extra tree scanning phase for `negate_iife`
- `negate_iife` now only deals with the narrowest form, i.e. IIFE sitting directly under `AST_SimpleStatement`
- `booleans`, `conditionals` etc. will now take care the rest via more accurate accounting
- `a(); void b();` => `a(); b();`

fixes #1288
closes #1451

test/compress/sequences.js

@@ -213,3 +213,41 @@ limit_2: {
         i, j, k;
     }
 }
+
+negate_iife_for: {
+    options = {
+        sequences: true,
+        negate_iife: true,
+    };
+    input: {
+        (function() {})();
+        for (i = 0; i < 5; i++) console.log(i);
+
+        (function() {})();
+        for (; i < 5; i++) console.log(i);
+    }
+    expect: {
+        for (!function() {}(), i = 0; i < 5; i++) console.log(i);
+        for (function() {}(); i < 5; i++) console.log(i);
+    }
+}
+
+iife: {
+    options = {
+        sequences: true,
+    };
+    input: {
+        x = 42;
+        (function a() {})();
+        !function b() {}();
+        ~function c() {}();
+        +function d() {}();
+        -function e() {}();
+        void function f() {}();
+        typeof function g() {}();
+    }
+    expect: {
+        x = 42, function a() {}(), function b() {}(), function c() {}(),
+        function d() {}(), function e() {}(), function f() {}(), function g() {}()
+    }
+}