ldconfig: small optimization

Swap which side of a comparison is byte-swapped by be32toh()
on little-endian architectures.

The be32toh() macro just returns the operand and big-endian
architectures and returns it byte-swapped on little-endian
architectures.

When operating on a constant argument, the compiler can perform
the swap operation at build time instead of swapping the data
read from the hints file at run time.

Reviewed by: kib
Tested by: tuexen
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D44734