Currently, we are doing the final module link (.ko) at different places
(Makefile.build vs Makefile.modver) depending on CONFIG_MODVERSIONS.
Apart from being confusing, that also means we have this code path
duplicated, and the modversions path most likely gets little testing.
    
It's actually cleaner to just do the final link from Makefile.modver always,
performance-wise it's not a noticable difference, since we don't descend
in that step, but just use the list of modules generated during the build.
    
This step is also preliminary for doing additional postprocessing, e.g.
generating module alias information from PCI / USB device tables.