-dtag-inference-checks flag is broken on the unregisterized backend.

See https://gitlab.haskell.org/ghc/ghc/-/jobs/1145537

The issue seems to be that the RTS function barf isn't in scope and we end up with:

/tmp/ghc317867_0/ghc_1.hc:1519:32: error:
     error: ‘barf’ undeclared (first use in this function); did you mean ‘nanf’?
     ghcFunPtr = ((void (*)(void *))barf);
                                    ^~~~
                                    nanf

Not sure if we should just emit a dummy prototype or add the appropriate include to the C code. Probably just do whatever we do for stg_gc_fun and friends. But it's fairly low priority so for now I just open a ticket instead.