Flag for late RELRO application

[Florian Weimer <fweimer@redhat.com>]

I would like to add a flag to gABI (visible in the dynamic section) 
which indicates that the loader shall apply RELRO protection only after 
running the ELF constructors from DT_INIT and DT_INIT_ARRAY.

This would allow applications to allocate a mapping and store a pointer 
to it in permanently read-only memory.  On the mapping itself, the 
application can set the protection flags (and keys) as needed.

Comments?

Thanks,
Florian