Currently: 1) libsodium and 2) nacl.
Note that the "nacl" variant is actually libsodium. We just want to make
sure the static analysers see the `VANILLA_NACL` code paths.
This flag isn't helpful for the most common case of aggregate
initialisation, namely `{0}`. We don't want to be writing `{{{0}}}` with
some brittle number of braces.
We used to have lots of these in the code, but now that all the endian
stuff is no longer dependent on host byte order, we can re-enable the
warning flag and catch any future violations.
