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/directmapnt.c

@@ -25,8 +25,9 @@
 #include "libc/runtime/directmap.h"
 #include "libc/sysv/consts/prot.h"
 
-textwindows struct DirectMap __mmap$nt(void *addr, size_t size, unsigned prot,
-                                       int64_t handle, int64_t off) {
+textwindows noasan struct DirectMap __mmap$nt(void *addr, size_t size,
+                                              unsigned prot, int64_t handle,
+                                              int64_t off) {
   struct DirectMap dm;
   if ((dm.maphandle = CreateFileMappingNuma(
            handle, &kNtIsInheritable,