build-system: Add 'clojure-build-system'.
* guix/build-system/clojure.scm, guix/build/clojure-build-system.scm: New
files.
* guix/build/clojure-utils.scm (@*, @@*): New macros.
(%source-dirs, %test-dirs, %compile-dir, %main-class, %omit-source?,
%aot-include, %aot-exclude, %tests?, %test-include, %test-exclude,
%clojure-regex): New variables.
(package-name->jar-names, canonicalize-relative-path, find-files*,
file-sans-extension, relative-path->clojure-lib-string, find-clojure-libs,
compiled-from?, include-list\exclude-list, eval-with-clojure, create-jar):
New procedures.
* Makefile.am (MODULES): Add them.
* doc/guix.texi (Build Systems): Document 'clojure-build-system'.
