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.

dsp/tty/write.c

@@ -38,8 +38,8 @@
  * @return 0 on success, or -1 w/ errno
  */
 ssize_t ttywrite(int fd, const void *data, size_t size) {
-  char *p;
   ssize_t rc;
+  const char *p;
   size_t wrote, n;
   p = data;
   n = size;