Fix warnings about:
. Unused variables
. format mismatch in printf/scanf format string and arguments
. Missing parenthesis around assignment as truth values
. Clang warnings anout unknown GCC pragma
NetBSD assumes off_t is 64-bit, but on MINIX it is still 32-bit.
So cast the calls to use big_off_t, as stat(2) uses.
Only used in warning messages, was not a real production bug.
