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/open.c

@@ -31,7 +31,7 @@
  * @asyncsignalsafe
  * @vforksafe
  */
-nodiscard int open(const char *file, int flags, ...) {
+int open(const char *file, int flags, ...) {
   va_list va;
   unsigned mode;
   va_start(va, flags);