https://bugs.freedesktop.org/show_bug.cgi?id=80584
--- Comment #6 from dex+fdobugzilla@dragonslave.de --- I think this may be due to missing GL_ARB_tessellation_shader extension.
Mesa lists this as Status "started" but no driver implementation yet.
I'll try to evaluate the status of this and see if I can verify that its indeed this missing extension.
(That would also mean that XCOM is in fact OpenGL)