Silence gcc asm deprectation warning in output.c.

gcc prefers asm parameters not be casts.
diff --git a/src/output.c b/src/output.c
index 28cb024..1637ffd 100644
--- a/src/output.c
+++ b/src/output.c
@@ -110,8 +110,9 @@
 static void
 puts_cs(u16 action, const char *s)
 {
-    for (;; s++) {
-        char c = GET_GLOBAL(*(u8*)s);
+    char *vs = (char*)s;
+    for (;; vs++) {
+        char c = GET_GLOBAL(*vs);
         if (!c)
             break;
         putc(action, c);