mesa: Fix transform feedback of unsubscripted arrays.

mesa: Fix transform feedback of unsubscripted arrays.

It is not explicitly stated in the GL 3.0 spec that transform feedback
can be performed on a whole varying array (without supplying a
subscript).  However, it seems clear from context that this was the
intent.  Section 2.15 (TransformFeedback) says this:

    When writing varying variables that are arrays, individual array
    elements are written in order.

And section 2.20.3 (Shader Variables), says this, in the description
of GetTransformFeedbackVarying:

    For the selected varying variable, its type is returned into
    type. The size of the varying is returned into size. The value in
    size is in units of the type returned in type.

If it were not possible to perform transform feedback on an
unsubscripted array, the returned size would always be 1.

This patch fixes the linker so that transform feedback on an
unsubscripted array is supported.

Fixes piglit tests "EXT_transform_feedback/builtin-varyings
gl_ClipDistance[{4,8}]-no-subscript" and
"EXT_transform_feedback/output_type *[2]-no-subscript".

Note: on back-ends that set
gl_shader_compiler_options::LowerClipDistance (for example i965),
tests "EXT_transform_feedback/builtin-varyings
gl_ClipDistance[{1,2,3,5,6,7}]" still fail.  I hope to address this in
a later patch.

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