CentOS/Fedora use annobin which will complain if FORTIFY_SOURCE=0
is used so we disable those checks to avoid the warnings.
We also make sure that when we query the compilation flags so we can
add more, we set _fortify_level=0 and undefine _lto_flags so that we
don't get those flags in the result.
Daan De Meyer
a2574ebf4d