Currently when the build fails (e.g. due to a missing named export), the message is pretty ugly:

<img width="1033" alt="screen shot 2017-11-04 at 13 12 31" src="https://user-images.githubusercontent.com/810438/32405680-d618d2e6-c161-11e7-9b91-e0241c7c3eed.png">

It would be nice to display the relevant line inline with syntax highlighting, sort of like Babel does it. Maybe Babel's `babel-code-frame` could be helpful (not sure).

To reproduce, fail the build by removing some `export` somewhere and run `yarn build`. (Tip: `yarn build core --type=NODE_DEV` is the fastest way to build just `packages/react/*` and that might be enough to reproduce and iterate on the error message.)

The relevant logic for displaying build errors is probably somewhere in `scripts/rollup/build.js`.

**If you'd like to work on this please comment here, so we don't have many people working on the same thing.**
if (warning.code === 'UNRESOLVED_IMPORT') {
    console.error(warning.message);
    process.exit(1);
  }
  if (warning.code === 'UNUSED_EXTERNAL_IMPORT') {
    const match = warning.message.match(/external module '([^']+)'/);
    if (!match || typeof match[1] !== 'string') {
      throw new Error(
        'Could not parse a Rollup warning. ' + 'Fix this method.'
      );
    }
    const importSideEffects = Modules.getImportSideEffects();
    const path = match[1];
    if (typeof importSideEffects[path] !== 'boolean') {
      throw new Error(
        'An external module "' +
          path +
          '" is used in a DEV-only code path ' +
          'but we do not know if it is safe to omit an unused require() to it in production. ' +
          'Please add it to the `importSideEffects` list in `scripts/rollup/modules.js`.'
      );
    }
    
    return;
  }
  console.warn(warning.message || warning);
}
function getRollupOutputOptions(