[v3] use -Wl,-z,relro if possible

[Paolo Carlini]

Paolo Carlini wrote:

>No progress. I can confirm that on my x86-linux machine (stock
>glibc-2.3.6, by the way) binutils-2.16.1 doesn't play well with
>--gc-sections.
>
>FWIW, I'm now using binutils-2.16.91.0.5 and with it, everything seems
>fine. No idea why...
>  
>
Benjamin, irrespective of my completely crazy troubles with 2.16.1, I
think there is another danger with enabling unconditionally
--gc-sections: some targets, at least with somewhat old binutils, may
not support --gc-sections at all, and the following warning is generated:

    /usr/bin/ld: Warning: gc-sections option ignored

thus, the testsuite completely fails :( For example I'm seeing that on
powerpc64-linux + binutils 2.15.90.0.1.1 (not really up to date, but
otherwise fine I think)

Paolo.