linker: Move global instructions from the linked shader first

For the shader containing 'main', use the linked shader (i.e., the
clone of the original shader that contained main) as the source for
global instructions to move into main.

src/glsl/linker.cpp

@@ -687,12 +687,16 @@ link_intrastage_shaders(struct gl_shader_program *prog,
    /* Move any instructions other than variable declarations or function
     * declarations into main.
     */
-   exec_node *insertion_point = (exec_node *) &main_sig->body;
+   exec_node *insertion_point =
+      move_non_declarations(linked->ir, (exec_node *) &main_sig->body, false,
+			    linked);
+
    for (unsigned i = 0; i < num_shaders; i++) {
+      if (shader_list[i] == main)
+	 continue;
+
       insertion_point = move_non_declarations(shader_list[i]->ir,
-					      insertion_point,
-					      (shader_list[i] != main),
-					      linked);
+					      insertion_point, true, linked);
    }
 
    /* Resolve initializers for global variables in the linked shader.