posix/flock: disable this class if under Windows

posix/flock.cpp

@@ -8,13 +8,14 @@
 
 #include "./flock.hpp"
 #include "./except.hpp"
+#include "../platform.hpp"
 
 #include <sys/file.h>
 
 using flock_  = cruft::posix::flock;
 
 
-
+#ifndef PLATFORM_WIN32
 ///////////////////////////////////////////////////////////////////////////////
 flock_::flock (cruft::posix::fd const &_fd, int const _operation)
     : flock (_fd.dup (), _operation)
@@ -58,4 +59,4 @@ flock_::native (void) const
 {
     return m_fd;
 }
-
+#endif