process: Improve the output of Debug for ExitStatus on Unix

[tgross35]

Currently Debug only prints the raw value:

ExitStatus(
    unix_wait_status(
        139,
    ),
)

That isn't very meaningful on its own since you may have to manually decode the value to understand what happened. Change the implementation to look more structural:

ExitStatus(
    unix_wait_status {
        value: 139,
        status: Signaled { signal: 11, name: SIGSEGV, core_dumped: true },
    },
)

This is a bit more similar to the information available via Display:

signal: 11 (SIGSEGV) (core dumped)

[rustbot]

r? @aapoalas

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[Mark-Simulacrum]

Any reason to be this verbose? Maybe we should just Debug as Display + the raw status code?

View changes since the review

[tgross35]

As in something like this?

ExitStatus(
    unix_wait_status {
        value: 139,
        message: "signal: 11 (SIGSEGV) (core dumped)"
    },
)

I think I have a mild preference for what's in the PR currently since it looks more like other Debug impls and doesn't use all that many more characters than the string (I made it intentionally not wrap with pretty printing). I don't feel especially strongly though.

[Mark-Simulacrum]

I was thinking something even shorter, e.g., "signal: 11 (SIGSEGV) (core dumped) (code: 139)"