Eliminate some flakes

- Get ASAN working on Windows.

- Deleting directories and then recreating them with the same name in a
  short period of time appears to be a no-no on Windows.

- There's no reason to call FlushFileBuffers on close() for pipes, and
  it's harmful since it might block indefinitely for no good reason.

libc/calls/winerr.greg.c

@@ -28,7 +28,7 @@
  * @return -1 w/ few exceptions
  * @note this is a code-size saving device
  */
-privileged int64_t __winerr(void) {
+privileged noasan int64_t __winerr(void) {
   if (IsWindows()) {
     errno = GetLastError();
     return -1;