Avoid minifying typeof x == 'undefined' checks into x === void 0.

Former-commit-id: 23c998b48a1d2e1bca19dad6bf16fa94aeebed31

build/minify.js

@@ -185,9 +185,10 @@
       var toplevel = uglifyJS.parse(source);
 
       // 2. compress
-      // // enable unsafe comparisons
+      // enable unsafe comparisons
       toplevel.figure_out_scope();
       toplevel = toplevel.transform(uglifyJS.Compressor({
+        'comparisons': false,
         'unsafe_comps': true,
         'warnings': false
       }));