* autoload.cc (NtSetSecurityObject): Add.

* fhandler_disk_file.cc (fhandler_disk_file::fchmod): Only request
	READ_CONTROL rights when opening the file.
	* ntdll.h (NtSetSecurityObject): Add declaration.
	* security.cc (write_sd): Call NtSetSecurityObject instead of
	BackupWrite.
	(get_nt_object_security): Don't free security descriptor here.

	* syscalls.cc (ttyname): Use buffer of length TTY_NAME_MAX + 1.
	* sysconf.cc (sysconf): Handle _SC_TTY_NAME_MAX request.
	* include/limits.h: Define TTY_NAME_MAX and _POSIX_TTY_NAME_MAX.

winsup/cygwin/sysconf.cc

@@ -122,6 +122,8 @@ sysconf (int in)
 	  }
       case _SC_RTSIG_MAX:
 	return RTSIG_MAX;
+      case _SC_TTY_NAME_MAX:
+        return TTY_NAME_MAX;
     }
 
   /* Invalid input or unimplemented sysconf name */