Add eclass/usr-ldscript.eclass to package automation

[krnowak]

CI: http://jenkins.infra.kinvolk.io:8080/job/container/job/sdk/1781/cldsv/

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It couldn't be added before to automation, because the eclass in Gentoo would introduce have unwanted side-effects into our built images. But the Gentoo version of the eclass is essentially a no-op when USE=split-usr is disabled. We have recently moved to use Gentoo profiles that disable USE=split-usr altogether, and with this move, we can now safely put the eclass into automation.

This marks the point where the entirety of the portage-stable is under automation.

Closes flatcar/Flatcar#645.
Closes flatcar/Flatcar#646.

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• Inspected CI output for image differences: /boot and /usr size, packages, list files for any missing binaries, kernel modules, config files, kernel modules, etc.

[krnowak]

This does not seem to be exactly a no-op change, though. But the changes seem to be minor - previously some packages were installing /usr/lib64/libfoo.so.1.2.3 (being a proper dynamic library), /usr/lib64/libfoo.so.1 (being a symlink to the libfoo.so.1.2.3), and /usr/lib64/libfoo.so (being some linker script). Now /usr/lib64/libfoo.so is also a symlink to libfoo.so.1.2.3 instead.

The linker script was fixing some linking issues that stemmed from the fact that some dynamic libraries were stored in /lib, whereas static libraries - in /usr/lib. This fix is clearly irrelevant, because we only have /usr/lib, and /lib is a symlink to the former. This means that the fix was for profiles that enabled USE=split-usr. We are not using such profiles anymore.

The reason that this change occurred now is because some ebuilds are calling gen_usr_ldscript function (which created those linker scripts, clobbering the libfoo.so -> libfoo.so.1.2.3 symlink) and this PR added the usr-ldscript.eclass which brings in the second definition of the function (and it clobbers the first one), and this function became essentially a no-op because it does an early return if USE=split-usr is disabled. The first definition came from toolchain-funcs.eclass', it's documented as deprecated and doesn't have the shortcut for USE=split-usrbeing disabled. So earlier,gen_usr_ldscriptfromtoolchain-funcs.eclasswas in use and it was generating linker scripts, nowgen_usr_ldscriptfromusr-ldscript.eclass` is in use and it does nothing.

[github-actions]

Build action triggered: https://github.com/flatcar/scripts/actions/runs/11347653651

[krnowak]

CI passed.