OpenBSD dynamic libraries never link to libc directly.
Instead, they have undefined symbols for all libc functions they use
that ld.so resolves to the libc referred to in the main executable.

Thus, disallowing undefined symbols will always fail

Nix fails to build on OpenBSD with a linking error due to a non-found
symbol in boehm-gc. Just disable the GC until we can find a proper
workaround.