third_party/murmurhash includes mongo/base and mongo/platform headers unnecessarily. It's doing this to access ConstDataView to get an unaligned endian swap.
Unfortunately that brings in a lot of mongo-specifics that can end up bringing in Abseil, and murmurhash isn't built with Abseil in its #include path.

So we're left with unwritten rules about which headers base and ConstDataView can include, or we can fix the layering violation in MurmurHash. I think we should inline the unaligned load and endian-swapping code into murmurhash since that's a pretty standard operation, and it's strange for a third_party library to reach out to mongo for support headers anyway.

I found this by adding stdx/unordered_map to base/init.h and getting a compile failure in murmurhash.