glsl: Add prototype for udivmod64()

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

src/compiler/glsl/builtin_functions.h

@@ -64,6 +64,9 @@ umul64(void *mem_ctx, builtin_available_predicate avail);
 ir_function_signature *
 sign64(void *mem_ctx, builtin_available_predicate avail);
 
+ir_function_signature *
+udivmod64(void *mem_ctx, builtin_available_predicate avail);
+
 }
 
 #endif /* BULITIN_FUNCTIONS_H */