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/sock/kntwsadata.c

@@ -17,6 +17,7 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/bits/weaken.h"
+#include "libc/calls/calls.h"
 #include "libc/calls/strace.internal.h"
 #include "libc/dce.h"
 #include "libc/mem/mem.h"
@@ -37,17 +38,16 @@
 hidden struct NtWsaData kNtWsaData;
 
 static textwindows void WinSockCleanup(void) {
-  size_t i;
-  STRACE("WSACleanup()");
-  WSACleanup();
-  for (i = 0; i < g_fds.n; ++i) {
+  int i, rc;
+  STRACE("WinSockCleanup()");
+  for (i = g_fds.n; i--;) {
     if (g_fds.p[i].kind == kFdSocket) {
-      if (weaken(free)) {
-        weaken(free)((struct SockFd *)g_fds.p[i].extra);
-        g_fds.p[i].extra = 0;
-      }
+      close(i);
     }
   }
+  // TODO(jart): Check WSACleanup() result code
+  rc = WSACleanup();
+  STRACE("WSACleanup() → %d% lm", rc);
 }
 
 textwindows noasan void WinSockInit(void) {