Wasmtime should always print guest panics

[tschneidereit]

Feature

Currently, Wasmtime doesn't always print anything to stderr when the guest panics: e.g. when serving incoming HTTP requests, panics are only printed if they happen before a response is sent. If the panic happens after the response headers have been sent, the panic is silently swallowed, and will only show up with the right WASMTIME_LOG incantation.

Benefit

Make guest panics easier to identify and debug.

Implementation

I'm not sure where this needs to be added, unfortunately.

Alternatives

Do nothing.

[alexcrichton]

Do you have an example to run? Glancing at the logging in wasmtime serve it looks like it's writing everything to stdout/stderr as soon as it gets it, so I'm not immediately sure where the issue might lie.