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/write-nt.c

@@ -42,7 +42,6 @@ textwindows ssize_t write$nt(struct Fd *fd, const struct iovec *iov,
                 iovlen ? clampio(iov[0].iov_len) : 0, &wrote,
                 offset2overlap(opt_offset, &overlap))) {
     if (!wrote) assert(!SumIovecLen(iov, iovlen));
-    FlushFileBuffers(fd->handle);
     return wrote;
   } else {
     return __winerr();