For those who are intested why this happens:
I ran into this but felt like getting to the bottom of it.
It appears that redhat 8.0 doesn't really uninstall postgres when you remove the database package via their gui. So if you remove the database package and then build and install postgres you have potentially two different versions running.
Unfortunately the redhat rpm has precedence on the path and when you call createlang there is some versionitis that happenes.
I removed the rpm postgres ( via rpm -e ) and my error went away. I'm not sure yet if there will be any fallout from this . If something goes wrong I'll add another answer here. I'm just trying to save the next person the time to figure out what is going wrong.
I ran the make installcheck and all seems to be ok now (although I had to delete the db and run inidb again for it to pass as it had an error on the first pass).
