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/calls.mk

@@ -44,7 +44,6 @@ LIBC_CALLS_A_DIRECTDEPS =				\
 	LIBC_NT_ADVAPI32				\
 	LIBC_NT_KERNEL32				\
 	LIBC_NT_NTDLL					\
-	LIBC_RAND					\
 	LIBC_STR					\
 	LIBC_STUBS					\
 	LIBC_SYSV_CALLS					\