utimecmp: avoid new GCC 7 warning from -Wbool-operation
Testing this module would fail when using GCC 7 like this:
$ CFLAGS='-O -Werror=bool-operation' ./gnulib-tool --create-testdir \
--dir=/tmp/x --with-tests --test utimecmp
../../gllib/utimecmp.c: In function ‘utimecmp’:
../../gllib/utimecmp.c:291:36: error: ‘~’ on a boolean expression \
[-Werror=bool-operation]
time_t s = src_s & ~ (res == 2 * BILLION);
^
../../gllib/utimecmp.c:370:16: error: ‘~’ on a boolean expression \
[-Werror=bool-operation]
src_s &= ~ (res == 2 * BILLION);
^
* lib/utimecmp.c (utimecmp): Do not apply "~" to a boolean.
Instead, make it explicit that we intend to apply it to 0 or 1.