broken macports gcc-mp-9 optimizer

[rurban]

see perl11/cperl@2b80a7e

in cperl I hardfail on gcc-mp-9 in darwin.
for XSConfig from cpan we could just remove the optimizer setting ' -O.'

or even find the root cause, but this could be tricky. But I'm afraid that gcc-mp-10 and maybe even on more platforms we will have the same problems, as the symptom is not at all platform related. Looks like a generic gcc optimizer bug to me.