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/runtime/print.greg.c

@@ -35,7 +35,6 @@ static void __print$nt(const void *data, size_t len) {
   savexmm(xmm + 128);
   hand = __imp_GetStdHandle(kNtStdErrorHandle);
   __imp_WriteFile(hand, data, len, &wrote, NULL);
-  __imp_FlushFileBuffers(hand);
   loadxmm(xmm + 128);
 }