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/directmap.c

@@ -33,8 +33,8 @@
  * bypassed by calling this function. However the caller is responsible
  * for passing the magic memory handle on Windows NT to CloseHandle().
  */
-noasan struct DirectMap sys_mmap(void *addr, size_t size, int prot, int flags,
-                                 int fd, int64_t off) {
+struct DirectMap sys_mmap(void *addr, size_t size, int prot, int flags, int fd,
+                          int64_t off) {
   /* asan runtime depends on this function */
   struct DirectMap d;
   if (!IsWindows() && !IsMetal()) {