vcs-svn: suppress a -Wtype-limits warning

vcs-svn: suppress a -Wtype-limits warning

On 32-bit architectures with 64-bit file offsets, gcc 4.3 and earlier
produce the following warning:

	    CC vcs-svn/sliding_window.o
	vcs-svn/sliding_window.c: In function `check_overflow':
	vcs-svn/sliding_window.c:36: warning: comparison is always false \
	    due to limited range of data type

The warning appears even when gcc is run without any warning flags
(this is gcc bug 12963).  In later versions the same warning can be
reproduced with -Wtype-limits, which is implied by -Wextra.

On 64-bit architectures it really is possible for a size_t not to be
representable as an off_t so the check this is warning about is not
actually redundant.  But even false positives are distracting.  Avoid
the warning by making the "len" argument to check_overflow a
uintmax_t; no functional change intended.

Reported-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>