OBSOLETE_BY does not prevent building

[xypron]

The OBSOLETE_BY value is used in do_install() to prevent installing a module that is no longer needed or supported since the specified kernel version.

But the module is still being built.

It does not make much sense to build a module that will never be installed:

• The source code may not be compatible to the new kernel source due to changed kernel APIs.
• Building may take a considerable time.

We should not build modules for kernels which match the OBSOLETE_BY version.

[evelikov]

The last related change I can see is from 2020 94a08e6 which was reverted shortly after - see 885f827.

Sadly neither the revert nor the PR #126 mention why - @GoPerry do you have any recollections?

@xypron do you have a git repo/project with an example of using OBSOLETE_BY? Can we interest you in writing a test and/or fix :-)