cmd/gc: fix printf format in typecheck.c

There are probably more of these, but bound and len are 64 bits so use %lld
in message about array index out of bounds.
Fixes the 386 build.

LGTM=bradfitz, rsc
R=rsc, bradfitz
CC=golang-codereviews, rickarnoldjr
https://golang.org/cl/66110043

src/cmd/gc/typecheck.c

@@ -2503,7 +2503,7 @@ typecheckcomplit(Node **np)
 				len = i;
 				if(t->bound >= 0 && len > t->bound) {
 					setlineno(l);
-					yyerror("array index %d out of bounds [0:%d]", len-1, t->bound);
+					yyerror("array index %lld out of bounds [0:%lld]", len-1, t->bound);
 					t->bound = -1;	// no more errors
 				}
 			}