[lldb][test] Avoid Windows import error in TestDriverWithClosedSTDIO.py

Test added in llvm#164905, skipped by llvm#165318, but that change did not
guard the import. This import is run when we parse the file which
happens before any skips are applied.

Author: DavidSpickett

lldb/test/API/driver/stdio_closed/TestDriverWithClosedSTDIO.py

@@ -8,7 +8,9 @@
 import os
 import sys
 import socket
-import fcntl
+
+if os.name != "nt":
+    import fcntl
 
 import lldbsuite.test.lldbutil as lldbutil
 from lldbsuite.test.lldbtest import *