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/reduce.c

@@ -382,7 +382,7 @@ reduce_grammar (void)
       reduce_print ();
 
       if (!bitset_test (N, accept->content->number - ntokens))
-        complain (&startsymbol_location, fatal,
+        complain (&startsymbol_loc, fatal,
                   _("start symbol %s does not derive any sentence"),
                   startsymbol->tag);