Don't abort in panic hook

[cole-miller]

This makes it impossible to catch_unwind, including in dependencies. There might be a reason I'm not thinking of to abort here; if so, we might want to consider building with panic=abort instead since this also decreases the binary size (and maybe helps compile times?).

Release Notes:

• N/A

[ConradIrwin]

The main thing to be sure is that the process still exits on a normal panic.

Catch unwind seems like a dangerous game in any case, but there are definitely good uses for it

[cole-miller]

The process will still exit on panic with this change, since the panic hook is called before unwinding begins. So I think we should do it if we value catch_unwind (in the few cases where it's appropriate to reach for it).

If we can (continue to) live without catch_unwind, switching to panic=abort has the following effect as measured (crudely) on my Linux machine:

panic setting	scratch debug build time	stripped release binary size
unwind	326s	205 MB
abort	289s (11% faster)	176 MB (14% smaller)

So I'm definitely somewhat tempted to go that route.