Move test for github issue 4345

The issue was a dependency cycle when a public library copies files from
a parent directory using copy_files. The test was that a readible error
message is produced in that situation, but it's not necessary that this
situation result in a dependency cycle at all.

This change moves the test case to its own file and now asserts that the
case doesn't result in an error.

Signed-off-by: Stephen Sherratt <stephen@sherra.tt>

test/blackbox-tests/test-cases/github4345.t

@@ -0,0 +1,11 @@
+This is a reproduction case from issue #4345
+  $ DIR="gh4345"
+  $ mkdir $DIR && cd $DIR
+  $ echo "(lang dune 2.8)" > dune-project
+  $ mkdir lib
+  $ touch lib.opam file lib/lib.ml
+  $ cat >lib/dune <<EOF
+  > (library (name lib) (public_name lib))
+  > (copy_files (files ../file))
+  > EOF
+  $ dune build --root .

test/blackbox-tests/test-cases/reporting-of-cycles.t/run.t

@@ -67,22 +67,3 @@ cryptic and can involve unrelated files:
   -> required by _build/default/indirect/a.exe
   -> required by alias indirect/indirect-deps in indirect/dune:6
   [1]
-
-This is a reproduction case from issue #4345
-  $ DIR="gh4345"
-  $ mkdir $DIR && cd $DIR
-  $ echo "(lang dune 2.8)" > dune-project
-  $ mkdir lib
-  $ touch lib.opam file lib/lib.ml
-  $ cat >lib/dune <<EOF
-  > (library (name lib) (public_name lib))
-  > (copy_files (files ../file))
-  > EOF
-  $ dune build --root .
-  Error: Dependency cycle between:
-     Computing installable artifacts for package lib
-  -> Evaluating predicate in directory _build/default
-  -> Computing directory contents of _build/default/lib
-  -> Computing installable artifacts for package lib
-  [1]
-  $ cd ..