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/calls/mkntcmdline.c

@@ -71,7 +71,6 @@ textwindows int mkntcmdline(char16_t cmdline[ARG_MAX / 2], char *const argv[]) {
   wint_t x, y;
   int slashes, n;
   bool needsquote;
-  char16_t cbuf[2];
   char *ansiargv[2];
   size_t i, j, k, s;
   if (!argv[0]) {