Fix multiversioning issues caused by the parallel llvm work (#52194)
So after struggling with this for a long while it seems there were two
different issues. The first one we lacked coverage over, but the other
was a very subtle issue when we sorted the fptrs.
~I still need to add test that does multiversioning where we call
between multiversioned functions~
Fixes https://github.com/JuliaLang/julia/issues/52079