Using Wasm coredump

The following steps describe how to debug using Wasm coredump in Wasmtime:

Compile your WebAssembly with debug info enabled; for example:
```
$ rustc foo.rs --target=wasm32-wasi -C debuginfo=2
```

foo.rs

fn c(v: usize) {
    a(v - 3);
}

fn b(v: usize) {
    c(v - 3);
}

fn a(v: usize) {
    b(v - 3);
}

pub fn main() {
    a(10);
}

Run with Wasmtime and Wasm coredump enabled:

$ wasmtime --coredump-on-trap=/tmp/coredump foo.wasm

thread 'main' panicked at 'attempt to subtract with overflow', foo.rs:10:7
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
Error: failed to run main module `foo.wasm`

Caused by:
    0: Core dumped at /tmp/coredump
    1: failed to invoke command default
    2: error while executing at wasm backtrace:
                ...

Use wasmgdb to debug:

$ wasmgdb foo.wasm /tmp/coredump

wasmgdb> bt
...
#13     000175 as panic () at library/core/src/panicking.rs
#12     000010 as a (v=???) at /path/to/foo.rs
#11     000009 as c (v=???) at /path/to/foo.rs
#10     000011 as b (v=???) at /path/to/foo.rs
#9      000010 as a (v=???) at /path/to/foo.rs
#8      000012 as main () at /path/to/foo.rs
...

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Using Wasm coredump

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