[RFH] gcc constant expression warning...

With the recent gcc, we get:

sha1_file.c: In check_packed_git_: sha1_file.c:527: warning: assuming signed overflow does not occur when assuming that (X + c) < X is always false sha1_file.c:527: warning: assuming signed overflow does not occur when assuming that (X + c) < X is always false

when compiling with

    -O2 -Werror -Wall -Wold-style-definition \
    -ansi -pedantic -std=c99 -Wdeclaration-after-statement

The offending lines are:

        if (idx_size != min_size) {
                /* make sure we can deal with large pack offsets */
                off_t x = 0x7fffffffUL, y = 0xffffffffUL;
                if (x > (x + 1) || y > (y + 1)) {
                        munmap(idx_map, idx_size);