add support for filtering dependencies by using False as version

[edmondac]

Useful for architecture-specific deps, e.g.:

dependencies = [
    ('VTK', {'arch=x86_64': '8.2.0', 'arch=POWER': False}, local_python_versionsuffix),
]

So in this example, on POWER don't include a VTK dependency at all

[akesandgren]

Hmm.... wouldn't it be enough to write

dependencies = [
    ('VTK', {'arch=x86_64': '8.2.0'}, local_python_versionsuffix),
]

to get that effect?
I.e., default being False?

And then we could perhaps do,

dependencies = [
    ('VTK', {'arch=default': '8.2.0', 'arch=POWER': False}, local_python_versionsuffix),
]

To only turn it off for POWER, or something, replace "default" with something better...

[edmondac]

Hmm.... wouldn't it be enough to write

dependencies = [
    ('VTK', {'arch=x86_64': '8.2.0'}, local_python_versionsuffix),
]

to get that effect?
I.e., default being False?

And then we could perhaps do,

dependencies = [
    ('VTK', {'arch=default': '8.2.0', 'arch=POWER': False}, local_python_versionsuffix),
]

To only turn it off for POWER, or something, replace "default" with something better...

I do agree with that, but those changes would be in a different part of the codebase, so I'd prefer not to do it in this PR if possible. The syntax for arch-specific deps exists already - I'm just adding support for specifying version=False (for any dep) so I can say "this arch doesn't want this dep at all".

[akesandgren]

Yes, I was just throwing out ideas...

[Flamefire]

I do like the arch=default idea however I'm strongly against the "implicit default" idea for the version: This will lead to skipping the dependency for an arch not yet added. So IMO this is good as-is and should be followed-up by the arch=default which allows the same but being explicit: {'arch=x86_64': '8.2.0', 'arch=default': False}

[akesandgren]

LGTM

[akesandgren]

Going in, thanks @edmondac!