Address alignment warnings for createcell68k()

createcell68k(typecode) returns a pointer that is aligned for the typecode
argument.  Changing the return type to "void *" puts the onus on the caller
to cast the result to an appropriately aligned object.  All current uses
in the maiko source ask for 4-byte objects (TYPE_FIXP, TYPE_FLOATP).

src/mkcell.c

@@ -90,7 +90,7 @@ retry:
 
 } /* N_OP_createcell end */
 
-DLword *createcell68k(unsigned int type) {
+void *createcell68k(unsigned int type) {
   struct dtd *dtd68k;
   DLword *ptr, *lastptr;
   LispPTR newcell;