[rfc][gold plugin] Fix pr19901

[Rafael Espíndola]

>> tools/lto is effectively the ld64 interface now. It works and it is
>> pretty stable, but don't expect many new features in that.
>
> Looks like we're using tools/lto (although doesn't that call lib/LTO?).

Yes, but tools/LTO is the stable interface. So if lib/LTO is changed,
tools/lto has to compensate for that. The flip side is that we have to
be a lot more conservative about which features show up in tools/lto.

Cheers,
Rafael