Merging ".o" files to one "kernel.o" can be convenient for further
linking, but it requires running `ld` directly. Running `ld` directly
sometimes runs into a mismatch between the C compiler and the default
`ld`. It's better to use the more typical approach of collecting
objects into an archive.
original commit: 7d5b60c7566570655e567495d86d546101cf8fb4