security/liboqs: fix build on powerpc64le

1. Add FreeBSD's name for 64-bit POWER little endian,
2. Don't use -Werror:
/wrkdirs/usr/ports/security/liboqs/work/liboqs-0.7.0/tests/ds_benchmark.h:142:45: error: implicit conversion from 'long' to 'double' may lose precision [-Werror,-Wimplicit-int-float-conversion]
        return (uint64_t)(time.tv_sec * 1e9 + time.tv_nsec);