@kha The runtime folder includes what is needed to link a
standalone Lean program. It is still contains some unnecessary files.
We will be able to remove them after we release Lean4.
The over-application doesn't occur very often in practice.
The new version adds an extra "copy" step, but it avoids the quadratic
blowup in code size.
Xavier Leroy reports that only 5% of all calls are over-applications
in his experiments.
In Lean3, 6.59% of all calls performed to compile corelib are "over",
and we did not implement any fancy optimization.
