fixing qhull: seems that dependency on cmake is essential when it is used

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

@@ -21,6 +21,8 @@ class Qhull(Package):
     # https://github.com/qhull/qhull/pull/5
     patch('qhull-iterator.patch', when='@1.0')
     
+    depends_on('cmake')
+
     def install(self, spec, prefix):
         with working_dir('spack-build', create=True):
             cmake('..', *std_cmake_args)