Fix warnings

This change fixes Cosmopolitan so it has fewer opinions about compiler
warnings. The whole repository had to be cleaned up to be buildable in
-Werror -Wall mode. This lets us benefit from things like strict const
checking. Some actual bugs might have been caught too.

libc/stdio/ctermid.c

@@ -42,6 +42,6 @@ char *ctermid(char *s) {
   if (s) {
     return strcpy(s, tty);
   } else {
-    return tty;
+    return (char *)tty;
   }
 }