The root tsconfig.build.json has `files: []` and only references the
packages, so `tsc --noEmit --project tsconfig.build.json` checked no file:
a type error added to a package source passed lint with exit code 0.
--build follows the references. It cannot be combined with --noEmit
(TS6310), so it writes the declarations the build writes; previous build
output is removed first, since package configs without an `include` pick
it up as source. Measured on the consumers: no new errors, 1-47 s.