i965/vec4: Add a brw->gen >= 6 assertion in three-source emitters.

Three source instructions didn't exist until Gen6.  vec4_generator has
assertions to catch this, but catching it in the visitor provides a
nicer backtrace.

Cc: "10.1" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Acked-by: Eric Anholt <eric@anholt.net>
1 file changed