glsl: support compilation of geometry shaders

This commit adds all of the parsing and semantics for GLSL 150 style
geometry shaders.

v2 (Paul Berry <stereotype441@gmail.com>): Adjust i965's
brw_link_shader() to pass the new is_geometry_shader argument to
do_set_program_inouts.  Add a few missing calls to
get_pipeline_stage().  Fix some signed/unsigned comparison warnings.
Fix handling of NULL consumer in assign_varying_locations().

v3 (Bryan Cain <bryancain3@gmail.com>): fix indexing order of 2D
arrays.  Also, allow interpolation qualifiers in geometry shaders.

v4 (Paul Berry <stereotype441@gmail.com>): Eliminate
get_pipeline_stage()--it is no longer needed thanks to 030ca23 (mesa:
renumber shader indices according to their placement in pipeline).
Remove 2D stuff.  Move vertices_per_prim() to ir.h, so that it will be
accessible from outside the linker.  Remove
inject_num_vertices_visitor.  Move use of geom_array_resize_visitor
prior to use of array_resizing_visitor.  Rework for GLSL 1.50.  Use a
single shader_type argument for do_set_program_inouts()
mesa: Refactor copying of linked program data.

This patch creates a single function to copy the the UsesClipDistance
flag from gl_shader_program.Vert to gl_vertex_program.  Previously
this logic was duplicated in the i965-specific function
brw_link_shader() and the core mesa function _mesa_ir_link_shader().

This logic will have to be expanded to support geometry shaders, and I
don't want to have to update it in two separate places.
mesa: Copy linked program data for GS.

The documentation for gl_shader_program.Geom and gl_geometry_program
says that the former is copied to the latter at link time, but this
wasn't happening.  This patch causes _mesa_ir_link_shader() to perform
the copy, and updates comment accordingly.
glsl: Require geometry shader inputs to be arrays.
glsl/linker: Properly error check VS-GS linkage.

From section 4.3.4 (Inputs) of the GLSL 1.50 spec:

    Geometry shader input variables get the per-vertex values written
    out by vertex shader output variables of the same names. Since a
    geometry shader operates on a set of vertices, each input varying
    variable (or input block, see interface blocks below) needs to be
    declared as an array.

Therefore, the element type of each geometry shader input array should
match the type of the corresponding vertex shader output.
glsl/linker: Properly pack GS input varyings.

Since geometry shader inputs are arrays (where the array index
indicates which vertex is being examined), varying packing needs to
treat them differently.
glsl: Modify varying packing to use a temporary exec_list.

This patch modifies lower_packed_varyings to store the packing code it
generates in a temporary exec_list, and then splice that list into the
shader's main() function when it's done.  This paves the way for
supporting geometry shader outputs, where we'll have to splice a clone
of the packing code before every call to EmitVertex().

As a side benefit, varying packing code is now emitted in the same
order for inputs and outputs; this should make debug output a little
easier to read.
glsl: Properly pack GS output varyings

In geometry shaders, outputs are consumed at the time of a call to
EmitVertex() (as opposed to all other shader types, where outputs are
consumed when the shader exits).  Therefore, when packing geometry
shader output varyings using lower_packed_varyings, we need to do the
packing at the time of the EmitVertex() call.

This patch accomplishes that by adding a new visitor class,
lower_packed_varyings_gs_splicer, which is responsible for splicing
the varying packing code into place wherever EmitVertex() is found.
mesa/shaderapi: Allow 0 GEOMETRY_VERTICES_OUT.

ARB_geometry_shader4 spec Errors:
"The error INVALID_VALUE is generated by ProgramParameteriARB if <pname>
is GEOMETRY_VERTICES_OUT_ARB and <value> is negative."

Reviewed-by: Paul Berry <stereotype441@gmail.com>
mesa: Validate the drawing primitive against the geometry shader input primitive type.

Reviewed-by: Paul Berry <stereotype441@gmail.com>
glsl/linker: Fail to link geometry shader without vertex shader.

From section 2.15 (Geometry Shaders) the OpenGL 3.2 spec:

    A program object that includes a geometry shader must also include
    a vertex shader; otherwise a link error will occur.

Reviewed-by: Paul Berry <stereotype441@gmail.com>
!UPSTREAM: glsl/linker: Fail if linking geometry shader with 0 GEOMETRY_VERTICES_OUT.

ARB_geometry_shader4 spec 2.15.2:
"Linking will also fail [...] if the program object contains objects to form a
geometry shader, and the value of GEOMETRY_VERTICES_OUT_ARB is zero."

Reviewed-by: Paul Berry <stereotype441@gmail.com>

TODO: May not be necessary for GLSL 1.50 style geometry shaders.  Make a test to validate.
main: Fix delete_shader_cb() for geometry shaders
st/mesa, glsl_to_tgsi: add support for geometry shaders

v2 (Bryan Cain <bryancain3@gmail.com>): fix 2D array indexing order.
gallivm: Fix indirect input fetches for gs.
gallium/draw: Pass primitive ID as integer to the shader.

The shader interprets the value as an integer.
mesa/st: Allow geometry shaders without gl_Position export.

From the ARB_geometry_shader4 spec (section Geometry Shader outputs):
"The built-in special variable gl_Position is intended to hold the
homogeneous vertex position. Writing gl_Position is optional."
!UPSTREAM: mesa: fix transform feedback when a geometry shader is active

TODO: test
!UPSTREAM: Fix up GS handling of gl_ClipDistance/gl_ClipVertex linkage rules.

TODO:
- Test
- Squash
!UPSTREAM: make stuff safe to include from C++

TODO:
- Split