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/close.c

@@ -53,8 +53,7 @@ int close(int fd) {
     rc = ebadf();
   }
   if (!__vforked && fd < g_fds.n) {
-    g_fds.p[fd].kind = kFdEmpty;
-    g_fds.f = MIN(g_fds.f, fd);
+    __releasefd(fd);
   }
   return rc;
 }