glsl: Move builtin_function related prototypes to a separate file

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>

src/compiler/glsl/ast_function.cpp

@@ -27,6 +27,7 @@
 #include "ir.h"
 #include "main/core.h" /* for MIN2 */
 #include "main/shaderobj.h"
+#include "builtin_functions.h"
 
 static ir_rvalue *
 convert_component(ir_rvalue *src, const glsl_type *desired_type);