Silence another warning in 1986/marshall

This warning was previously not possible to silence but by changing the
(alt) code slightly (with same functionality including indeed the
problem I documented in compilers.md) it now is.

1986/marshall/marshall.alt.c

@@ -10,5 +10,5 @@ x  ;if    (P(  !        i              )        |  cc[  !      j ]
 &  P(j    )>2  ?        j              :        i  ){*  argv[i++ +!-i]
 ;              for    (i=              0;;    i++                   );
 _exit(argv[(int)*argc-2/cc[1*(int)*argc]|-1<<4]);printf("%d",P(""));}}
-  P  (    a  )   char a   ;  {    a  ;   while(    a  >      "  B   "
+  P  (    a  )   char a   ;  {    a  ;   while((char *)a  >   "  B   "
   /* -    by E            ricM    arsh             all-      */);    }