* 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/ntdll.h

@@ -412,6 +412,8 @@ extern "C"
   					PSECURITY_DESCRIPTOR, ULONG, PULONG);
   NTSTATUS NTAPI NtQueryVirtualMemory (HANDLE, PVOID, MEMORY_INFORMATION_CLASS,
 				       PVOID, ULONG, PULONG);
+  NTSTATUS NTAPI NtSetSecurityObject (HANDLE, SECURITY_INFORMATION,
+				      PSECURITY_DESCRIPTOR);
   NTSTATUS NTAPI NtUnmapViewOfSection (HANDLE, PVOID);
   VOID NTAPI RtlInitUnicodeString (PUNICODE_STRING, PCWSTR);
   ULONG NTAPI RtlNtStatusToDosError (NTSTATUS);