style: use consistently *_loc for locations

Some members are called foo_location, others are foo_loc.  Stick to
the latter.

* src/gram.h, src/location.h, src/location.c, src/output.c,
* src/parse-gram.y, src/reader.h, src/reader.c, src/reduce.c,
* src/scan-gram.l, src/symlist.h, src/symlist.c, src/symtab.h,
* src/symtab.c:
Use _loc consistently, not _location.

src/reader.h

@@ -32,7 +32,7 @@ typedef struct merger_list
   struct merger_list* next;
   uniqstr name;
   uniqstr type;
-  location type_declaration_location;
+  location type_declaration_loc;
 } merger_list;
 
 /* From the parser.  */