Download checksum verification fails on FreeBSD 13.1

[edolnx]

Describe the bug When attempting to download the golang archive on FreeBSD 13 the checksum fails to verify with the following error:

verifying checksum
sha256sum: option requires an argument -- c
usage: sha256sum [-pqrtx] [-c file] [-s string] [files ...]
Authenticity of package archive can not be assured. Exiting.

This can be worked around by temporarily renaming the sha256sum tool to sha256sum.fbsd and re-running the installer.

To Reproduce Steps to reproduce the behavior:

1. On a FreeBSD 13.1 amd64 system, attempt to asdf install golang 1.17.13
2. See error

Expected behavior This seems to be due to an incompatibility of the between the FreeBSD 13 and Linux versions of the sha256sum tool. Temporarily renaming the sha256sum binary and re-running the command worked. Looking at the code, if sha256sum is not found the shasum tool is used instead. I have also tested on an older FreeBSD install (11.4) which does not include the sha256sum tool and everything works as expected.

Additional context Since this is a bug specific to newer versions of FreeBSD, I am unsure how best to resolve this issue which is why I am opening a bug instead of submitting a PR to correct it. It may make more sense to simply use only the shasum tool on the FreeBSD platform, or it may make more sense to simply try that tool first in all cases? I'm happy to do the PR for whatever the discussion of this issue feels is appropriate.