TNS-38: ignore dependency on self, for CLJS

In Clojure (.clj) code, a namespace depending on itself makes no sense.
But it is perfectly reasonable for a ClojureScript (.cljs) file to
depend on a Clojure (.clj) file for macro definitions in the same
namespace, via :require-macros.

More generally, this means that a "namespace" is logically defined in
multiple files, which tools.namespace does not yet handle.

This causes spurious circular-dependency error in tools. See, for
example, clojure-emacs/refactor-nrepl#127

It is easy to work around the specific case of self-dependency via
:require-macros, which has no meaning anywhere else.

As a consequence, tools.namespace will no longer throw an exception if
an ordinary Clojure namespace tries to :require itself.

src/main/clojure/clojure/tools/namespace/parse.cljc

@@ -123,6 +123,9 @@
 (defn deps-from-ns-decl
   "Given an (ns...) declaration form (unevaluated), returns a set of
   symbols naming the dependencies of that namespace.  Handles :use and
-  :require clauses but not :load."
+  :require clauses but not :load. Ignores a namespace depending on
+  itself, for example a .cljs file with :require-macros on the .clj
+  file of the same namespace."
   [decl]
-  (set (mapcat deps-from-ns-form decl)))
+  (disj (set (mapcat deps-from-ns-form decl))
+        (name-from-ns-decl decl)))