LTO fallback without error

[PhilipDeegan]

Hi,

I was wondering if there was any way to not fail if LTO is in use, but just fallback to what it would be without mold?

Thanks

[rui314]

That's an interesting question. I've never thought of that before, but we can indeed fall back to GNU ld or LLVM lld if LTO is in use. We can just invoke these linkers with the exact same command line arguments as mold received.

There are a few concerns, though:

1. It may be "too automatic". If a user is using mold, it is their intentional choice. Automatic fallback may not desirable for them.
2. It could change the link result in an edge case, as mold, GNU ld and LLVM lld all behave slightly differently in edge cases. That should be very rare, though.

But automatic fallback is an attractive idea... Let me think about that more.

[rui314]

OK, I decided to implement automatic fallback. We should support LTO natively in the future, but in the meantime, this should work as a poor-man's replacement.