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/runtime/getinterpreterexecutablename.c

@@ -45,10 +45,8 @@
  */
 char *GetInterpreterExecutableName(char *p, size_t n) {
   int e;
-  size_t m;
   int cmd[4];
   ssize_t rc;
-  char *r, *t;
   e = errno;
   if (n < 2) {
     errno = ENAMETOOLONG;