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/package.lisp

@@ -1,6 +1,7 @@
 ;;;  package.lisp --- packages description
 
 ;;;  Copyright (C) 2006, 2007, 2008, 2009, 2010 by Walter C. Pelissero
+;;;  Copyright (C) 2021 by the TVL Authors
 
 ;;;  Author: Walter C. Pelissero <walter@pelissero.de>
 ;;;  Project: sclf
@@ -179,6 +180,7 @@
 	   #:stat-mode
 	   #:save-file-excursion
 	   #:stat-modification-time
+	   #:stat-creation-time
 	   #:file-modification-time
 	   #:file-creation-time
 	   #:show