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/str/strncpy.c

@@ -60,6 +60,7 @@
  * @return dest
  * @see stpncpy(), memccpy()
  * @asyncsignalsafe
+ * @vforksafe
  */
 char *strncpy(char *dest, const char *src, size_t stride) {
   size_t i;