build: use the system lib luajit for s390x

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Hi, @ThomasDevoogdt, this PR will allow the system luajit lib to be used on s390x, please help to merge it before this Thursday!
I am giving a demo in the fluent bit community meeting this week for fluent#7286, hope we can get fluent#7286 merged this week with both your and my changes!

Thanks in advance!

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