Improve synchronization

- Fix bugs in kDos2Errno definition
- malloc() should now be thread safe
- Fix bug in rollup.com header generator
- Fix open(O_APPEND) on the New Technology
- Fix select() on the New Technology and test it
- Work towards refactoring i/o for thread safety
- Socket reads and writes on NT now poll for signals
- Work towards i/o completion ports on the New Technology
- Make read() and write() intermittently check for signals
- Blinkenlights keyboard i/o so much better on NT w/ poll()
- You can now poll() files and sockets at the same time on NT
- Fix bug in appendr() that manifests with dlmalloc footers off

libc/runtime/clone.c

@@ -97,7 +97,7 @@ privileged int clone(int (*f)(void *), void *stack, int flags, void *arg, ...) {
                  : "memory");
     unreachable;
   } else if (IsWindows()) {
-    if ((tidfd = __reservefd()) == -1) return -1;
+    if ((tidfd = __reservefd(-1)) == -1) return -1;
     if (flags == CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND) {
       if ((hand = CreateThread(&kNtIsInheritable, 0, NT2SYSV(WinThreadMain),
                                &(struct WinThread){f, arg, stack}, 0, &tid))) {