cairo: ensure that X support is disabled for variant "~X" (#4242)

* cairo: ensure that X support is disabled for variant "~X"

* cairo: explicitly enable X support for +X variant

* cairo: prefer "variant in spec" over spec.satisfies(variant)

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

@@ -51,4 +51,8 @@ class Cairo(AutotoolsPackage):
     def configure_args(self):
         args = ["--disable-trace",  # can cause problems with libiberty
                 "--enable-tee"]
+        if '+X' in self.spec:
+            args.extend(["--enable-xlib", "--enable-xcb"])
+        else:
+            args.extend(["--disable-xlib", "--disable-xcb"])
         return args