build: explicitly set `noEmit: false` in the build script

What's the problem this PR addresses?

https://github.com/yarnpkg/berry/pull/6133 (cc @clemyan) enabled noEmit by default which caused yarn pack to not get any build output.

How did you fix it?

Explicitly set noEmit: false in the build script.

Checklist

[x] I have read the Contributing Guide.
[x] I have set the packages that need to be released for my changes to be effective.
[x] I will check that all automated PR checks pass before the PR gets reviewed.

yarnpkg / berry