test: glob_files_rec with a relative path

We demonstrate that using relative paths in [glob_files_rec] has
unintended consequences. In this test, we install some artifacts outside
the package directory just by globbing from a parent dir.

Signed-off-by: Rudi Grinberg <me@rgrinberg.com>

<!-- ps-id: 0f38b0df-b5b3-4797-a555-8687aed27290 -->

Author: rgrinberg

test/blackbox-tests/test-cases/install/install-glob/install-glob-relative.t

@@ -0,0 +1,33 @@
+Install a glob pattern from a relative path
+
+  $ cat >dune-project <<EOF
+  > (lang dune 3.6)
+  > (package (name foo))
+  > EOF
+
+  $ mkdir -p stanza stuff/xy
+  $ touch stuff/foo.txt stuff/xy/bar.txt
+
+  $ cat >stanza/dune <<EOF
+  > (install
+  >  (files (glob_files_rec ../stuff/*.txt))
+  >  (section share))
+  > EOF
+
+  $ dune build foo.install
+  $ cat _build/default/foo.install
+  lib: [
+    "_build/install/default/lib/foo/META"
+    "_build/install/default/lib/foo/dune-package"
+  ]
+  share: [
+    "_build/install/default/share/stuff/foo.txt" {"../stuff/foo.txt"}
+    "_build/install/default/share/stuff/xy/bar.txt" {"../stuff/xy/bar.txt"}
+  ]
+
+  $ dune install foo --prefix _foo
+  $ find _foo | sort | grep stuff
+  _foo/share/stuff
+  _foo/share/stuff/foo.txt
+  _foo/share/stuff/xy
+  _foo/share/stuff/xy/bar.txt