Using wuffs-c (not wuffs) is awkward

[nigeltao]

The wuffs command line tool is used when working on Wuffs-the-Library. The wuffs-c command line tool is (implicitly) part of that, but it can also be used on its own for other code written in Wuffs-the-Language, including code that doesn't live in this repository.

Doing that works... sort of. But it's not a great experience. The hello-wuffs-c example has to declare a placeholder wuffs-base.c file (as it can't rely on the generated gen/c/wuffs-base.c file), and the C driver program has to #define WUFFS_CONFIG__MODULE__BASE.

Both of these workarounds shouldn't be necessary.