When building the rust stuff we were getting the following compiler
error

  error: failed to run `rustc` to learn about target-specific information

  ...

    --- stderr
    error: Error loading target specification: Could not find specification for target "wasm32-wasi". Run `rustc --print target-list` for a list of built-in targets

This is due to wasm32-wasi being renamed to wasm32-wasip1, with
wasm32-wasi being kept clear for an eventual WASI 1.0 release.

Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

The programs demonstrate handling requests with payloads larger than
4GiB which means they need to be written out to disk and so also
demonstrates the use of the file-system access mechanism.

Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

When I renamed it from minimal to hello-world, it stopped being built
due to the make target name being the same as the directory name
(hello-world).

Rename the make target to rust-hello-world which also matches the naming
of the rest of the targets.

Fixes: 656c036 ("examples/rust: Add a minimal hello world rust example")
Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

This is about the smallest it can be.

Its Unit application config would look like

    "applications": {
        "rust-hello-world": {
            "type": "wasm",
            "module": "/path/to/unit-wasm/examples/rust/hello-world/target/wasm32-wasi/debug/rust_hello_world.wasm",
            "request_handler": "uwr_request_handler",
            "malloc_handler": "luw_malloc_handler",
            "free_handler": "luw_free_handler"
        }
    }

Signed-off-by: Andrew Clayton <a.clayton@nginx.com>

libunit-wasm and example C and Rust WebAssembly modules for NGINX Unit.

Co-developed-by: Timo Stark <t.stark@nginx.com>
Co-developed-by: Liam Crilly <liam@nginx.com>
Signed-off-by: Andrew Clayton <a.clayton@nginx.com>