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/runtime.h

@@ -72,6 +72,7 @@ void __print_string(const char *);
 void __fast_math(void);
 void *sbrk(intptr_t);
 int brk(void *);
+int NtGetVersion(void);
 
 /*───────────────────────────────────────────────────────────────────────────│─╗
 │ cosmopolitan § runtime » optimizations                                   ─╬─│┼