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: add EXT_geometry_shader4 and ARB_geometry_shader4 to extension list
mesa: account for geometry shader texture fetches in update_texture_state
glcpp: define extension macros for EXT/ARB_geometry_shader4
glsl: add builtins for EXT/ARB_geometry_shader4
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.
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.
glsl: support compilation of geometry shaders via EXT/ARB_geometry_shader4

This commit adds all of the parsing and semantics for EXT/ARB_geometry_shader4,
including support for 2D arrays as inputs.

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.
st/mesa, glsl_to_tgsi: add support for geometry shaders

Note (Paul Berry <stereotype441@gmail.com>): I'm not sure I rebased
this correctly.  It appears that some amount of 2D array support was
added to tgsi after the patch was originally written.
draw: account for separate shader objects in geometry shader code

The geometry shader code seems to have been originally written with the
assumptions that there are the same number of VS outputs as GS outputs and
that VS outputs are in the same order as their corresponding GS inputs. Since
TGSI uses separate shader objects, these are both wrong assumptions. This
was causing several valid vertex/geometry shader combinations to either render
incorrectly or trigger an assertion.
draw: use geometry shader info in clip_init_state if appropriate
WIP: make vec4_visitor::vp more generic
WIP: make vs_vec4_visitor class
WIP: move run() to vs_vec4_visitor
WIP: split brw_vs_compile out to brw_vec4_compile
i965: Consign COORD_REPLACE VS hacks to Pre-Gen6.

Pre-Gen6, the SF thread requires exact matching between VS output
slots (aka VUE slots) and FS input slots, even when the corresponding
VS output slot is unused due to being overwritten by point coordinate
replacement (glTexEnvi(GL_POINT_SPRITE, GL_COORD_REPLACE, GL_TRUE)).
As a result, we have a special hack in the VS to ensure when any
texture coordinate is subject to point coordinate replacement, it is
always allocated space in the VUE, even if it isn't written to by the
VS.

This hack isn't needed from Gen6 onwards, since SF (Gen7: SBE)
swizzling has the ability to insert the point coordinate into
gl_TexCoord[] without needing a corresponding unused VUE slot.

Note that no modification of SF setup code is required for this
patch--get_attr_override() already does the right thing.  However, we
make a slight comment change to clarify why this works.

In addition to eliminating unnecessary VS recompiles and saving
precious URB space on Gen6+, this will save us the trouble of having
to adjust this hack when we implement geometry shaders.
WIP: split brw_vs_prog_key
WIP: move emit_vertex_program_code() to vs_vec4_visitor
WIP: move setup_vp_regs() to vs_vec4_visitor
WIP: move get_vp_src_reg() to vs_vec4_visitor