root: require +opengl when +aqua is on (spack#47349)

According to root-project/root#7160, if
`-Dcocoa=ON` build must also be configured with `-Dopengl=ON`, since
otherwise the build encounters missing includes. This is/was a silent
failure in ROOT CMake, but I believe has been made an explicit failure
some time this year.

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

@@ -429,6 +429,8 @@ class Root(CMakePackage):
     # Incompatible variants
     if sys.platform == "darwin":
         conflicts("+opengl", when="~x ~aqua", msg="root+opengl requires X or Aqua")
+        # https://github.com/root-project/root/issues/7160
+        conflicts("+aqua", when="~opengl", msg="+aqua requires OpenGL to be enabled")
     else:
         conflicts("+opengl", when="~x", msg="root+opengl requires X")
     conflicts("+math", when="~gsl", msg="root+math requires GSL")