[testsuite] don't use lto plugin if it doesn't work

[Richard Guenther]

On Thu, Jun 28, 2012 at 4:08 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> On Thu, Jun 28, 2012 at 07:03:37AM -0700, Mike Stump wrote:
>> > Also, this scenario of silently deciding whether or not to use the
>> > linker plugin could bring us to different test results for the same
>> > command lines.  I don't like that.
>>
>> Right, which is why the static configuration of the host system at build
>> time is forever after an invariant.  The linker is smelled, it doesn't
>> support plugins, therefore we can't ever use it, therefore we never build
>> it...
>
> THis test is not about whether to build the plugin, but whether to force
> using it by default.  And to be able to use it by default, you need a
> guarantee that all the linkers you'll use it with do support the plugin.
> Therefore, if the build-time linker doesn't support it, I think it is just
> fine not all of your linkers support the plugin and not enable it by
> default.

I'd like to have a more reliable way to enable/disable the default use
of the linker-plugin then.  Something in config.gcc maybe, or at least
a flag I can specify at configure time.  If the default in config.gcc is
detected to not work then explicitely changing that (or confirming it)
would be required - otherwise we'd error out.

Richard.