glsl: add tessellation shader defines and built-in variables.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/glsl/shader_enums.h

@@ -152,7 +152,7 @@ typedef enum
     * \name Geometry shader system values
     */
    /*@{*/
-   SYSTEM_VALUE_INVOCATION_ID,
+   SYSTEM_VALUE_INVOCATION_ID,  /**< (Also in Tessellation Control shader) */
    /*@}*/
 
    /**
@@ -165,6 +165,17 @@ typedef enum
    SYSTEM_VALUE_SAMPLE_MASK_IN,
    /*@}*/
 
+   /**
+    * \name Tessellation Evaluation shader system values
+    */
+   /*@{*/
+   SYSTEM_VALUE_TESS_COORD,
+   SYSTEM_VALUE_VERTICES_IN,    /**< Tessellation vertices in input patch */
+   SYSTEM_VALUE_PRIMITIVE_ID,   /**< (currently not used by GS) */
+   SYSTEM_VALUE_TESS_LEVEL_OUTER, /**< TES input */
+   SYSTEM_VALUE_TESS_LEVEL_INNER, /**< TES input */
+   /*@}*/
+
    SYSTEM_VALUE_MAX             /**< Number of values */
 } gl_system_value;