[build] Use -z ignore instead of --as-needed on Solaris

[Tobias Burnus]

Rainer Orth wrote:
> While the Solaris linker doesn't support the --as-needed/--no-as-needed
> options (yet), it long has provided the equivalent -z ignore/-z record
> options.  This patch makes use of them, avoiding unnecessary
> dependencies on libgcc_s.so.1.

Could you also do a similar update in libgfortran/acinclude.m4's 
libgfor_cv_have_as_needed check?

Thanks,

Tobias