glsl: During linking, record whether a GS uses EndPrimitive().

glsl: During linking, record whether a GS uses EndPrimitive().

This information will be useful in the i965 back end, since we can
save some compilation effort if we know from the outset that the
shader never calls EndPrimitive().

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>