Optimize webpack rebuild speed (facebook#5065)

Derived from facebook#4492 (comment)

Author: Timer

scripts/build.js

@@ -142,7 +142,9 @@ function build(previousFileSizes) {
       if (err) {
         return reject(err);
       }
-      const messages = formatWebpackMessages(stats.toJson({}, true));
+      const messages = formatWebpackMessages(
+        stats.toJson({ all: false, warnings: true, errors: true })
+      );
       if (messages.errors.length) {
         // Only keep the first error. Others are often indicative
         // of the same problem, but confuse the reader with noise.