Re: Tree-walker callbacks vs -Wdeprecated-non-prototype

As visible on seawasp and locally (16/main branch nightly packages),
they decided to start warning about these casts with a new strict
variant of the warning.  Their discussion:

https://reviews.llvm.org/D134831

There are also a few other cases unrelated to this thread's original
problem, for example casts involving pg_funcptr_t, HashCompareFunc.  I
guess our options would be to turn that warning off, or reconsider and
try shoving the cast of "generic" arguments pointers down into the
functions?