compiler: use `OnceCell` from std
Fixes#76192
The only remaining direct use of `lazy_static` crate is in `src/bootstrap` but I am not sure how I can remove that dependency for now.
r? @matklad
Fixes#75050
Previously, we would unconditionally suppress the panic hook during
proc-macro execution. This commit adds a new flag
-Z proc-macro-backtrace, which allows running the panic hook for
easier debugging.