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/lower_vertex_id.cpp

@@ -37,6 +37,7 @@
 #include "ir_builder.h"
 #include "linker.h"
 #include "program/prog_statevars.h"
+#include "builtin_functions.h"
 
 namespace {