Fix CO:RE support for RHEL 8 and derivatives

[NeonSludge]

This PR fixes CO:RE support in tracee-ebpf on RHEL 8 and its derivatives.
RedHat kernel support was added some time ago by #351 but additional changes are now needed to make that fix work for CO:RE since this mode doesn't use actual RedHat Linux kernel header files and some definitions are missing.

[rafaeldtinoco]

LGTM.

$ RHEL_MAJOR=$(grep -Eoh -m 1 '[0-9]+\.[0-9]+' /etc/redhat-release | cut -d '.' -f 1)
$ RHEL_MINOR=$(grep -Eoh -m 1 '[0-9]+\.[0-9]+' /etc/redhat-release | cut -d '.' -f 2)
$ echo $(($RHEL_MAJOR << 8 | $RHEL_MINOR))
2052

@yanivagman I'll give a chance for @yanivagman to review this and merge if he is ok.

[yanivagman]

LGTM, thanks @NeonSludge!

[itaysk]

Shouldn't we've updated automatic compilation in main.go as well?

[yanivagman]

Not sure I understand correctly what you mean. but this change is only relevant to the CO-RE binary, so I don't think there should be any impact on the compilation steps in main.go

[itaysk]

Thanks for the clarification, I didn't understand that before. I still think we should make the compilation methods identical (they were before CORE) to reduce bug potential.

[yanivagman]

main.go shouldn't build co-re object, as it shouldn't be built on the target (this is the whole point of CO-RE).
I don't see any problem here, and no reason to put this logic in main.go