Build Python with Tkinter support

var/spack/repos/builtin/packages/tcl/package.py

@@ -44,6 +44,12 @@ def url_for_version(self, version):
 
     depends_on('zlib')
 
+    def setup_environment(self, spack_env, env):
+        # When using Tkinter from within spack provided python+tk, python
+        # will not be able to find Tcl/Tk unless TCL_LIBRARY is set.
+        env.set('TCL_LIBRARY', join_path(self.prefix.lib, 'tcl{0}'.format(
+                self.spec.version.up_to(2))))
+
     def install(self, spec, prefix):
         with working_dir('unix'):
             configure("--prefix=%s" % prefix)