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/mapanon.c

@@ -59,6 +59,8 @@ noasan void *mapanon(size_t size) {
   /* asan runtime depends on this function */
   void *m;
   m = mmap(0, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
-  if (m == MAP_FAILED && weaken(__oom_hook)) weaken(__oom_hook)(size);
+  if (m == MAP_FAILED && weaken(__oom_hook)) {
+    weaken(__oom_hook)(size);
+  }
   return m;
 }