* errno.cc (errmap): Map ERROR_BAD_NET_RESP to ENOSYS.

* fhandler_disk_file.cc (fhandler_disk_file::facl): Handle ENOSYS and
	point to  the explanation.
	* ntdll.h (STATUS_NOT_IMPLEMENTED): Define.
	* path.cc (symlink_info::check): Handle the inability of NT4 to use
	FileNetworkOpenInformation on share root dirs in either direction.
	* path.h (slash_unc_prefix_p): Remove unused declaration.
	* security.cc (get_info_from_sd): Handle ENOSYS from get_file_sd.
	Explain when this happens.

winsup/cygwin/path.h

@@ -343,8 +343,6 @@ class path_conv
 /* Interix symlink marker */
 #define INTERIX_SYMLINK_COOKIE  "IntxLNK\1"
 
-int __stdcall slash_unc_prefix_p (const char *path) __attribute__ ((regparm(1)));
-
 enum fe_types
 {
   FE_NADA = 0,		/* Nothing special */