style: avoid %{...%} in our parser

* src/parse-gram.y (%{...%}): Split in %code and %code requires.
* src/location.h: Add missing includes for self containedness.

src/location.h

@@ -20,6 +20,10 @@
 #ifndef LOCATION_H_
 # define LOCATION_H_
 
+# include <stdbool.h>
+# include <stdio.h>
+# include <string.h> /* strcmp */
+
 # include "uniqstr.h"
 
 /* A boundary between two characters.  */