[RFC] [gold] Simplify relocation strategy logic

[Cary Coutant]

> I don't believe this is correct.  ABSOLUTE_REF is defined as:
>
>    // A reference to the symbol's absolute address.  This includes
>    // references that cause an absolute address to be stored in the GOT.
>    ABSOLUTE_REF = 1,
>
> and the final symbol reference (by the GOT entry) is absolute
> in all these cases.  ("Absolute in GOT" was supposed to mean
> "an absolute reference _in_ the global offset table", not "to".)
> Whether the reference to the GOT entry itself is absolute, relative
> to the GP, or relative to the PC, isn't modelled by these flags.
>
> Does the patch rely on this, or was it just something you noticed
> by inspection?

My understanding of the ABI is that R_X86_64_GOTPCREL is a pc-relative
relocation to the GOT entry, and R_X86_64_GOTPLT64 is an absolute
reference to a GOT entry. In both cases, I believe the GOT entry
itself is expected to contain an absolute address. I rely on these
flags modeling the reference to the GOT entry, not the GOT entry
itself, and I think they're correct as they stand (although I'll
definitely take a closer look before committing to this). I'll fix the
comments, though.

-cary