parse-gram: update the Bison interface

* src/parse-gram.y (%pure-parser, %name-prefix): Replace with...
(%define api.pure, %define api.prefix)
* src/location.h, src/scan-gram.h: Adjust to api.prefix.

src/location.h

@@ -88,7 +88,7 @@ typedef struct
 
 } location;
 
-#define YYLTYPE location
+#define GRAM_LTYPE location
 
 #define EMPTY_LOCATION_INIT {{NULL, 0, 0}, {NULL, 0, 0}}
 extern location const empty_location;