glsl: Simplify the built-in function linking code.

Previously, we stored an array of up to 16 additional shaders to link,
as well as a count of how many each shader actually needed.

Since the built-in functions rewrite, all the built-ins are stored in a
single shader.  So all we need is a boolean indicating whether a shader
needs to link against built-ins or not.

During linking, we can avoid creating the temporary array if none of the
shaders being linked need built-ins.  Otherwise, it's simply a copy of
the array that has one additional element.  This is much simpler.

This patch saves approximately 128 bytes of memory per gl_shader object.

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

src/glsl/builtin_functions.cpp

@@ -609,8 +609,7 @@ builtin_builder::find(_mesa_glsl_parse_state *state,
     * that the "no matching signature" error will list potential candidates
     * from the available built-ins.
     */
-   state->builtins_to_link[0] = shader;
-   state->num_builtins_to_link = 1;
+   state->uses_builtin_functions = true;
 
    ir_function *f = shader->symbols->get_function(name);
    if (f == NULL)