[build, lto] Only accept -fuse-linker-plugin if linker supports -plugin (PR lto/46944)

[Rainer Orth]

Richard Guenther <rguenther@suse.de> writes:

>> I'm using gld 2.21, and -flto automatically uses the linker plugin, as
>> seen with -v.  Despite that, -plugin-opt=-fresolution=ldl.res is passed
>> to collect2/ld, but no ldl.res file is created.  In truss, I see a stat
>> of that file, but nothing more.
>
> Interesting - it works for me with both GNU ld and gold from binutils 
> 2.21.

Strange indeed.  Maybe related to using xgcc -B./ from a build tree?
gold still doesn't fully work for me, perhaps it does for this example.
I'll give that a try too.

>> > Can you update your patch with the tri-state solution?
>> 
>> Sure if the solution is deemed acceptable.  There isn't much point in
>> following that route if you see problems up front.
>
> If that solution avoids 3) then yes, I'm fine with going that route.
> Both 1) and 2) are very desirable anyway.

Ok, I'll update the patch over the weekend.

Thanks.
	Rainer

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Rainer Orth, Center for Biotechnology, Bielefeld University