Assertion failed since clang12 (mongodb42)

Hi,

I'm maintaining some databases/mongodb* ports.
On aarch64/14-CURRENT they started failing since the llvm/clang12 update.

See: http://www.ipv6proxy.net/go.php?u=http://ampere2.nyi.freebsd.org/data/main-arm64-default/pf44e1c1de734_s63ca9ea4f3/logs/errors/mongodb42-4.2.14.log

And look for:
Assertion failed: (isa<X>(Val) && "cast<Ty>() argument of incompatible type!"), function cast, file /usr/local/poudriere/jails/main-arm64/usr/src/contrib/llvm-project/llvm/include/llvm/Support/Casting.h, line 269.


This does not happen with LLVM 11 or on AMD64.
Can anybody point me in the right direction for fixing this?

Regards,
Ronald.