LinuxVersion::compare reported two versions as equal if it could
find a new '.' in the first version but not in the second.
But this is clearly wrong because it skips comparision of the valid last
part.

The comparision 5.16.12 >= 5.18 returned true because compare
reported the version as equal after comparing the first parts and
finding a second '.' in the first but not the second.

Fix this behavior by marking the current position as the last but
do not skip its comparision.

Add tests for the desired behaviour.

LinuxVersion used the assumption that both strings have the same
amount of dot-separated components.
But this is obviously not always the case.
If we can't compare the two strings further they must been equal so far.

* remove fancy but broken static LinuxVersion object.
  This means each usage of a EMPER_LINUX_* macro results in a syscall.
  But I think this is worth it when the result is a sound program.
  Users of those macros should store the result of the comparison anyway.
* fix that we skipped parsing the last part of a version string
* add a test for LinuxVersion
* IO_MUST_INVALIDATE_BROKEN_CHAIN can still be const

Move io and lib related tests into io/ and lib/.

Our test dictionaries not must have a 'source' key with an array
created with files().
This ensures we use always correct paths regardless of the actual directory
we are currently in.

Until https://github.com/mesonbuild/meson/issues/8608 is not solved
we have to separately specify the tests name in a 'name' key.