Set OLD_ICONV on Cygwin.

Cygwin still has old definition for the iconv() second
parameter. This patch fixes the last warning on Cygwin.
This has been tested with Cygwin 1.5.24.

Signed-off-by: Pascal Obry <pascal@obry.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -444,6 +444,7 @@ ifeq ($(uname_O),Cygwin)
 	NEEDS_LIBICONV = YesPlease
 	NO_FAST_WORKING_DIRECTORY = UnfortunatelyYes
 	NO_TRUSTABLE_FILEMODE = UnfortunatelyYes
+	OLD_ICONV = UnfortunatelyYes
 	# There are conflicting reports about this.
 	# On some boxes NO_MMAP is needed, and not so elsewhere.
 	# Try commenting this out if you suspect MMAP is more efficient