paraview: add some extra arguments on OS X

X shouldn't be used on OS X and spack expects a Unix-style install, not
a .app bundle.

var/spack/packages/paraview/package.py

@@ -60,6 +60,10 @@ def nfeature_to_bool(feature):
 
             feature_args.extend(std_cmake_args)
 
+            if 'darwin' in self.spec.architecture:
+                feature_args.append('-DVTK_USE_X:BOOL=OFF')
+                feature_args.append('-DPARAVIEW_DO_UNIX_STYLE_INSTALLS:BOOL=ON')
+
             cmake('..',
                 '-DCMAKE_INSTALL_PREFIX:PATH=%s' % prefix,
                 '-DBUILD_TESTING:BOOL=OFF',