Put static pointers to vec[234]_types along with the static float_type.

Otherwise you have to type a lot of get_instance.
diff --git a/ir_variable.cpp b/ir_variable.cpp
index a2c0803..ba91d56 100644
--- a/ir_variable.cpp
+++ b/ir_variable.cpp
@@ -137,10 +137,8 @@
     * FINISHME: value of GL_MAX_TEXTURE_COORDS.  GL_MAX_TEXTURE_COORDS must be
     * FINISHME: at least 2, so hard-code 2 for now.
     */
-   const glsl_type *const vec4_type =
-      glsl_type::get_instance(GLSL_TYPE_FLOAT, 4, 1);
    const glsl_type *const vec4_array_type =
-      glsl_type::get_array_instance(vec4_type, 2);
+      glsl_type::get_array_instance(glsl_type::vec4_type, 2);
 
    add_variable("gl_TexCoord", ir_var_out, vec4_array_type, instructions,
 		symtab);
@@ -219,10 +217,8 @@
     * FINISHME: value of GL_MAX_TEXTURE_COORDS.  GL_MAX_TEXTURE_COORDS must be
     * FINISHME: at least 2, so hard-code 2 for now.
     */
-   const glsl_type *const vec4_type =
-      glsl_type::get_instance(GLSL_TYPE_FLOAT, 4, 1);
    const glsl_type *const vec4_array_type =
-      glsl_type::get_array_instance(vec4_type, 2);
+      glsl_type::get_array_instance(glsl_type::vec4_type, 2);
 
    add_variable("gl_TexCoord", ir_var_in, vec4_array_type, instructions,
 		symtab);
@@ -237,10 +233,8 @@
     * FINISHME: value of GL_MAX_DRAW_BUFFERS.  GL_MAX_DRAW_BUFFERS must be
     * FINISHME: at least 1, so hard-code 1 for now.
     */
-   const glsl_type *const vec4_type =
-      glsl_type::get_instance(GLSL_TYPE_FLOAT, 4, 1);
    const glsl_type *const vec4_array_type =
-      glsl_type::get_array_instance(vec4_type, 1);
+      glsl_type::get_array_instance(glsl_type::vec4_type, 1);
 
    ir_variable *const fd =
       add_variable("gl_FragData", ir_var_out, vec4_array_type, instructions,