glsl: Enable various extensions for geometry shaders.

Allow the following extensions in geometry shaders:
- ARB_shader_texture_lod
- ARB_shading_language_packing
- ARB_texture_cube_map_array
- ARB_texture_multisample
- ARB_texture_rectangle
- ARB_uniform_buffer_object
- EXT_texture_array

Note: In principle there's no reason geometry shaders couldn't support
OES_texture_3D and OES_EGL_image_external, but it seems silly to
enable them, since these are GLSL ES extensions, and geometry shaders
aren't allowed in GLSL ES.
main: Fix geometry shader error messages (missing right paren)
main: Allow for the possibility of GL 3.2 without ARB_geometry_shader4.

Previously, we assumed that the only way Mesa would expose geometry
shader support was via the ARB_geometry_shader4 extension.  But this
extension has some extra complications over GL 3.2 (interactions with
compatibility-only features, and link-time initialization of the
constant gl_VerticesIn).  So we want to allow for the possibility of
supporting GL 3.2 (with GLSL 1.50 style geometry shaders) even if
ctx->Extensions.ARB_geometry_shader4 is false.

This patch adds a new function, _mesa_has_geometry_shaders(), which
returns true if either ARB_geometry_shader4 is supported or the GL
version is at least 3.2 desktop.  It also adds a new constant,
GeometryShaders150, which the driver can set to true to inform the
front-end that it supports GLSL 1.50-style geometry shaders.
!UPSTREAM ===== BEGIN rebase of Plombo's GS patches =====
draw/gs: fix allocation of buffer for GS output vertices

Before, it accounted for the size of the vertices but not the other fields
in the vertex_header struct, which caused memory corruption.
mesa: account for geometry shader texture fetches in update_texture_state
mesa/st: Add VARYING_SLOT_TEX[1-7] to st_translate_geometry_program().

v2 (Paul Berry <stereotype441@gmail.com>: Split out to separate patch
(previously this was part of "glsl: add builtins for geometry
shaders.")
!UPSTREAM: glsl: add builtins for geometry shaders.

v2 (Paul Berry <stereotype441@gmail.com>): Account for rework of
builtin_variables.cpp.  Use INTERP_QUALIFIER_FLAT for gl_PrimitiveID
so that it will obey provoking vertex conventions.  Convert to GLSL
1.50 style geometry shaders.
glsl: add ir_emitvertex and ir_endprim instruction types

These correspond to the EmitVertex and EndPrimitive functions in GLSL.

v2 (Paul Berry <stereotype441@gmail.com>): Add stub implementations of
new pure visitor functions to i965's vec4_visitor and fs_visitor
classes.
!UPSTREAM: glsl: lower gl_ClipDistanceIn to gl_ClipDistanceInMESA in lower_clip_distance

This corresponds to the lowering of gl_ClipDistance to gl_ClipDistanceMESA.
It converts the 2D array gl_ClipDistanceIn from EXT/ARB_geometry_shader4 to
a 1D array of vec4s, gl_ClipDistanceInMESA.

v2 (Paul Berry <stereotype441@gmail.com>): Fix indexing order for
gl_ClipDistanceIn lowering.  Properly lower bulk assignment of
gl_ClipDistanceIn[i].

TODO: May need to rework for GLSL 1.50.
!UPSTREAM: 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.  Partial rework for GLSL 1.50.

TODO:
- may need to rework for GLSL 1.50.
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.
!UPSTREAM: glsl: Require geometry shader inputs to be arrays.

TODO: may need rework for GLSL 1.50.
glsl/linker: Properly error check VS-GS linkage.

From the ARB_geometry_shader4 specification:

    A geometry shader may also read from an input varying variable declared
    with the "varying in" qualifiers. The value read will be the same value as
    written by the vertex shader for that varying variable. Since a geometry
    shader operates on primitives, each input varying variable needs to be
    declared as an array. Each element of such an array corresponds to a
    vertex of the primitive being processed. If the varying variable is
    declared as a scalar or matrix in the vertex shader, it will be a
    one-dimensional array in the geometry shader.

Therefore, a user-defined geometry shader input will always be an
array, and the *element type* of that 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>