glsl: geom shader max_vertices layout must match.

From GLSL 4.5 spec, "4.4.2.3 Geometry Outputs".
"all geometry shader output vertex count declarations in a
program must declare the same count."

Fixes:
GL45-CTS.geometry_shader.output.conflicted_output_vertices_max

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Cc: "11.2 12.0" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>

src/compiler/glsl/ast.h

@@ -368,7 +368,8 @@ public:
 
    bool process_qualifier_constant(struct _mesa_glsl_parse_state *state,
                                    const char *qual_indentifier,
-                                   unsigned *value, bool can_be_zero);
+                                   unsigned *value, bool can_be_zero,
+                                   bool must_match = false);
 
    void merge_qualifier(ast_layout_expression *l_expr)
    {