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/calls/readv-serial.c

@@ -37,7 +37,9 @@ static int GetFirstIov(struct iovec *iov, int iovlen) {
 ssize_t sys_readv_serial(struct Fd *fd, const struct iovec *iov, int iovlen) {
   size_t i;
   if ((i = GetFirstIov(iov, iovlen)) != -1) {
-    while (!IsDataAvailable(fd)) asm("pause");
+    while (!IsDataAvailable(fd)) {
+      __builtin_ia32_pause();
+    }
     ((char *)iov[i].iov_base)[0] = inb(fd->handle);
     return 1;
   } else {