The new option `set_option debug.skipKernelTC true` is meant for
temporarily working around kernel performance issues.
It compromises soundness because a buggy tactic may produce an invalid
proof, and the kernel will not catch it if the new option is set to true.
Remark: I had to comment
```
if debug.skipKernelTC.get opts then
addDeclWithoutChecking env decl
else
```
because the build was crashing when trying to compile Lake.
Going to perform `update-stage0` and try again.
