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/writev-serial.c

@@ -24,7 +24,9 @@ ssize_t sys_writev_serial(struct Fd *fd, const struct iovec *iov, int iovlen) {
   size_t i, j, wrote = 0;
   for (i = 0; i < iovlen; ++i) {
     for (j = 0; j < iov[i].iov_len; ++j) {
-      while (!(inb(fd->handle + UART_LSR) & UART_TTYTXR)) asm("pause");
+      while (!(inb(fd->handle + UART_LSR) & UART_TTYTXR)) {
+        __builtin_ia32_pause();
+      }
       outb(fd->handle, ((char *)iov[i].iov_base)[j]);
       ++wrote;
     }