We have it. Daniel Stone said the #ifdef HAVE_CONFIG_H comes from the
X11 transition to the modular build, where in the imake -> modular
build transition config.h wasn't universally available. Now we just
make this a requirement (so yeah Android better generate one too).

v2: Improve commit message a bit.

Reviewed-by: Eric Anholt <eric@anholt.net>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Arkadiusz Hiler <arkadiusz.hiler@intel.com>
Acked-by: Petri Latvala <petri.latvala@intel.com>
Acked-by: Daniel Stone <daniels@collabora.com>
Acked-by: Radoslaw Szwichtenberg <radoslaw.szwichtenberg@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>