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

[Rainer Orth]

Richard Guenther <richard.guenther@gmail.com> writes:

>> I think if the plugin linker is different from the normal linker we should
>> set HAVE_LTO_PLUGIN to 2.
>
> I think we should do the linker version checks which relate to linker-plugin
> use on the plugin-linker instead.  So if I specify a separate but known

I'll see if this is reasonably doable...

> buggy linker I don't want it to be used by default.

... but how about a different route for 4.7?  I've never really
understood the point of --with-plugin-ld.  Given that we have known-good
linkers, why not simply remove that wart?

	Rainer

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Rainer Orth, Center for Biotechnology, Bielefeld University