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

[Richard Guenther]

On Fri, Mar 18, 2011 at 10:26 AM, Rainer Orth
<ro@cebitec.uni-bielefeld.de> wrote:
> Richard Guenther <rguenther@suse.de> writes:
>
>>> Ok for mainline if that passes, and perhaps also the 4.6 branch?
>>
>> I'm ok with this for mainline - Paolo, can you double-check the
>> autofoo stuff?  As for 4.6 I'd like to give it a day or two on
>> trunk to allow people to report problems.
>
> The patch has been on mainline for two days now and I'm not aware of any
> problems.  Unless someone objects, I'm going to apply it to 4.6 branch
> later today.

It seemed to have disabled linker-plugin support for old binutils
with --with-plugin-ld=/usr/local/bin/gold, explicit -fuse-linker-plugin says
it is not supported.  The system linker does not have plugin support
(nor gold).  /usr/local has gold from binutils 2.20.50.xxx.  So it seems that

    # Allow -fuse-linker-plugin to enable plugin support in GNU gold 2.20.
    elif test "$ld_is_gold" = yes -a "$ld_vers_major" -eq 2 -a
"$ld_vers_minor" -eq 20; then
      gcc_cv_lto_plugin=1
    fi

only allows explicit -fuse-linker-plugin for recent gold but based on checking
the system linker version (instead of that of --with-plugin-ld).  I'd say
allow explicit -fuse-linker-plugin always if --with-plugin-ld is specified.

Richard.