Detect built ins in externals

[dav-is]

We should detect if the module is built in

https://github.com/zeit/ncc/blob/master/src/index.js#L121

[github-actions]

Stats from current PR

Click to expand stats

	zeit/next.js canary	zeit/next.js add-built-ins	Change
Build Duration	11.8s	11.7s	-101ms
node_modules Size	43.9 MB	43.9 MB	⚠️ +423 B
Total Bundle (main, webpack, commons) Size	210 kB	210 kB	✓
Total Bundle (main, webpack, commons) gzip Size	68.5 kB	68.5 kB	✓
Client _app Size	2.49 kB	2.49 kB	✓
Client _app gzip Size	1.04 kB	1.04 kB	✓
Client _error Size	9.66 kB	9.66 kB	✓
Client _error gzip Size	3.52 kB	3.52 kB	✓
Client pages/index Size	298 B	298 B	✓
Client pages/index gzip Size	235 B	235 B	✓
Client pages/link Size	3.28 kB	3.28 kB	✓
Client pages/link gzip Size	1.49 kB	1.49 kB	✓
Client pages/routerDirect Size	426 B	426 B	✓
Client pages/routerDirect gzip Size	304 B	304 B	✓
Client pages/withRouter Size	408 B	408 B	✓
Client pages/withRouter gzip Size	293 B	293 B	✓
Client main Size	24.4 kB	24.4 kB	✓
Client main gzip Size	7.89 kB	7.89 kB	✓
Client commons Size	183 kB	183 kB	✓
Client commons gzip Size	59.4 kB	59.4 kB	✓
Client webpack Size	1.49 kB	1.49 kB	✓
Client webpack gzip Size	774 B	774 B	✓
Base Rendered Size	1.34 kB	1.34 kB	✓
Build Dir Size	580 kB	580 kB	✓

Click to expand serverless stats

	zeit/next.js canary	zeit/next.js add-built-ins	Change
Build Duration	13.2s	13.2s	-48ms
node_modules Size	43.9 MB	43.9 MB	⚠️ +423 B
Total Bundle (main, webpack, commons) Size	210 kB	210 kB	✓
Total Bundle (main, webpack, commons) gzip Size	68.5 kB	68.5 kB	✓
Client _app Size	2.49 kB	2.49 kB	✓
Client _app gzip Size	1.04 kB	1.04 kB	✓
Client _error Size	9.66 kB	9.66 kB	✓
Client _error gzip Size	3.52 kB	3.52 kB	✓
Client pages/index Size	298 B	298 B	✓
Client pages/index gzip Size	235 B	235 B	✓
Client pages/link Size	3.28 kB	3.28 kB	✓
Client pages/link gzip Size	1.49 kB	1.49 kB	✓
Client pages/routerDirect Size	426 B	426 B	✓
Client pages/routerDirect gzip Size	304 B	304 B	✓
Client pages/withRouter Size	408 B	408 B	✓
Client pages/withRouter gzip Size	293 B	293 B	✓
Client main Size	24.4 kB	24.4 kB	✓
Client main gzip Size	7.89 kB	7.89 kB	✓
Client commons Size	183 kB	183 kB	✓
Client commons gzip Size	59.4 kB	59.4 kB	✓
Client webpack Size	1.49 kB	1.49 kB	✓
Client webpack gzip Size	774 B	774 B	✓
Serverless pages/link Size	338 kB	338 kB	✓
Serverless pages/link gzip Size	87.4 kB	87.4 kB	-1 B
Serverless pages/index Size	330 kB	330 kB	✓
Serverless pages/index gzip Size	85.5 kB	85.5 kB	-1 B
Serverless pages/_error Size	331 kB	331 kB	✓
Serverless pages/_error gzip Size	85.3 kB	85.3 kB	✓
Serverless pages/routerDirect Size	331 kB	331 kB	✓
Serverless pages/routerDirect gzip Size	85.5 kB	85.5 kB	-1 B
Serverless pages/withRouter Size	331 kB	331 kB	✓
Serverless pages/withRouter gzip Size	85.6 kB	85.6 kB	-1 B
Build Dir Size	2.12 MB	2.12 MB	✓