Unset NO_C99_FORMAT on Cygwin.

This should only be set based on the capability of your
compiler/library to support c99 format specifiers. In this
case the version of gcc/newlib and indirectly the version
of Cygwin. It should probably only be set in your config.mak
file.

Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Signed-off-by: Junio C Hamano <junkio@cox.net>

Makefile

@@ -378,7 +378,6 @@ ifeq ($(uname_O),Cygwin)
 	NO_STRCASESTR = YesPlease
 	NO_SYMLINK_HEAD = YesPlease
 	NEEDS_LIBICONV = YesPlease
-	NO_C99_FORMAT = YesPlease
 	NO_FAST_WORKING_DIRECTORY = UnfortunatelyYes
 	NO_TRUSTABLE_FILEMODE = UnfortunatelyYes
 	# There are conflicting reports about this.