Make registration of preprocessing passes explicit (#2564)

Make registration of preprocessing passes explicit (#2564)

As it turns out, self-registering types are problematic with static
linkage [0]. Instead of fixing the issue with linker flags, which seems
possible but also brittle (e.g. the flags may be different for different
linkers), this commit adds an explicit registration of each
preprocessing pass.

[0] https://www.bfilipek.com/2018/02/static-vars-static-lib.html