building glibc with gold linker & -frecord-gcc-switches results in internal error

[Cary Coutant]

> For a string merge section we don't really have to scan the relocs--if
> there are any relocs at all, something weird is going on.
> Output_section::add_merge_input_section already supports having
> add_input_section return false to mean that the section should be
> handled as a normal section rather than a merge section.

As it turns out, add_merge_input_section already refuses to handle it
as a merge section if reloc_shndx > 0, so we're good here.

We just need to gracefully handle the GOT reloc in a non-allocated section.

-cary