Constified code_loc_gen

node.h

@@ -137,7 +137,7 @@ typedef struct rb_code_location_struct {
 } rb_code_location_t;
 
 static inline rb_code_location_t
-code_loc_gen(rb_code_location_t *loc1, rb_code_location_t *loc2)
+code_loc_gen(const rb_code_location_t *loc1, const rb_code_location_t *loc2)
 {
     rb_code_location_t loc;
     loc.beg_pos = loc1->beg_pos;