parse.gperf: make memcpy() call happy

Hopefully this doesn't break anything; I'm struggling to
understand how this stuff works.

src/parse.gperf

@@ -304,5 +304,5 @@ void parse_one_option(struct cfginfo *restrict tmpcfg, const char *str, const ch
     exit(53);
   }
 
-  memcpy(offset+(char*)tmpcfg, &opt, sizeof(char*)); /* FIXME: This causes a warning; should it be 'sizeof(char)', or do we need to have the warning suppressed? -bjk 2021.10.14 */
+  memcpy((char**) (offset + (char*) tmpcfg), &opt, sizeof(char*));
 }