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

test/libc/calls/fcntl_test.c

@@ -17,6 +17,7 @@
 │ PERFORMANCE OF THIS SOFTWARE.                                                │
 ╚─────────────────────────────────────────────────────────────────────────────*/
 #include "libc/calls/calls.h"
+#include "libc/dce.h"
 #include "libc/fmt/fmt.h"
 #include "libc/log/check.h"
 #include "libc/macros.internal.h"
@@ -40,9 +41,12 @@ TEST(fcntl_getfl, testRemembersAccessMode) {
 }
 
 TEST(fcntl_setfl, testChangeAppendStatus) {
+  if (IsWindows()) {
+    // no obivous way to do fcntl(fd, F_SETFL, O_APPEND)
+    return;
+  }
   int fd;
   char buf[8] = {0};
-  if (IsWindows()) return; /* doesn't appear possible on windows */
   ASSERT_NE(-1, (fd = open("foo", O_CREAT | O_RDWR, 0644)));
   EXPECT_EQ(3, write(fd, "foo", 3));
   EXPECT_NE(-1, lseek(fd, 0, SEEK_SET));