wasmtime-wasi-c contains many bindgen-generated symbols like
bindgen_test_layout___wasi_event_t___wasi_event_u___wasi_event_u_fd_readwrite_t
that contain triple-underscores in them. rustc doesn't consider those
names snake-case and generates extensive warnings about them. Suppress
those warnings with allow(non_snake_case).
While the "__wasi_memory" name is something we considered, the name
currently being used for the memory exported to WASI is "memory", so
adjust the error message accordingly.
Surfaced when running sunfishcode/misc-tests. When trying to
truncate the file without the __WASI_RIGHT_PATH_FILESTAT_SET_SIZE
right, error __WASI_ENOTCAPABLE was correctly returned, however,
the guest fd pointer was not encoded to -1 in that case. This
commit fixes it by taking out the guest fd encoding out of the
conditional branch which turns out obsolete.
This adds the C WASI implementation as a new crate, wasmtime-wasi-c,
and adds a command-line flag to the wasmtime command-line driver to
select which WASI implementation to use.
