You're really abusing `builddependencies` here, doesn't make sense.

I'm not sure how to tackle this, to be honest. Want you actually want is something like `optional_dependencies`, i.e. stuff that only gets included when it is available. But, that gets in the way of the reproducibility we're so keen on.

Adding them in `builddependencies` doesn't really make them optional: the build will fail if any of them is not around.

Currently, we have no suitable way of handling something like this, other than creating two `biodeps` easyconfigs, e.g. one with a versionsuffix like `-strict` (or somsuch), and one without. But that's also not really what you want here, because that would force you to pick one of both in easyconfigs where you use the `biodeps` 'toolchain'.

My recommendation: add the ones currently listed in `builddependencies` to `dependencies`; since EasyBuild provides support for all of them anyway, I see no harm in including all of them, even if they're only `SHOULD`. And just having one `biodeps` easyconfigs (per toolchain, no versionsuffix) is good enough too then.