Greatly expand system() shell code features

The cosmopolitan command interpreter now has 13 builtin commands,
variable support, support for ; / && / || syntax, asynchronous support,
and plenty of unit tests with bug fixes.

This change fixes a bug in posix_spawn() with null envp arg. strace
logging now uses atomic writes for scatter functions. Breaking change
renaming GetCpuCount() to _getcpucount(). TurfWar is now updated to use
the new token bucket algorithm. WIN32 affinity masks now inherit across
fork() and execve().

libc/sock/sendto.c

@@ -52,7 +52,7 @@
  * @asyncsignalsafe
  * @restartable (unless SO_RCVTIMEO)
  */
-ssize_t sendto(int fd, const void *buf, size_t size, uint32_t flags,
+ssize_t sendto(int fd, const void *buf, size_t size, int flags,
                const struct sockaddr *opt_addr, uint32_t addrsize) {
   ssize_t rc;
   uint32_t bsdaddrsize;