gold input section handling

[David Miller]

When trying to build a sparc64 Linux kernel with my sparc gold target
I get an assertion failure in Output_data_dynamic::set_info_section().

The reason is that the input objects to the link are using different
section flags for a particular section.

The section '.devinit.data' in one object uses just SHF_ALLOC, and in
another it used (SHF_ALLOC | SHF_WRITE).

Gold doesn't like this, as it uses the flags as a unique key for
output section lookup.

The BFD linker allows this, and simply or's together all of the input
instance's section flags in the output section's flags.