feat(3p/lisp/sclf): build using buildLisp

Adding the default.nix is quite straightforward, however we have to make
today's SBCL happy: due to package locking it no longer likes sclf using
an sb-impl internal constant for some reason. This is however a good
opportunity to clean up the stat-*-time code: It converted the times in
an implementation specific way even though time.lisp does provide a
generic way to convert between unix and universal time. Note that the
updated ASDF file is untested, but should be a trivial enough change.

Change-Id: If193bf830ac704cc53e0855d8e9fff2b5a5ef291
Reviewed-on: https://cl.tvl.fyi/c/depot/+/3268
Tested-by: BuildkiteCI
Reviewed-by: grfn <grfn@gws.fyi>

third_party/lisp/sclf/OWNERS

@@ -0,0 +1,3 @@
+inherited: true
+owners:
+  - sterni