Invalid UTF-8 was detected in one or more arguments

Running a WASM file with a binary argument, such as:
```
wasmtime run hmac_md5 --key `printf "\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa"` "String to hash"
```
or
```
wasmtime run hmac_md5 -- --key `printf "\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa\xaa"` "String to hash"
```

Aborts execution with the following error:

```
error: Invalid UTF-8 was detected in one or more arguments
```

I see three problems with this:
1. There is no standard I'm aware of that requires the arguments to be textual
2. There is no standard that requires them to be UTF-8 encoded
3. Wasmtime is doing unneeded work while validating the arguments, and/or converting them to UTF-8