TLS GOT Relocations + Addends

[lenary]

Following on from #188

There are some more HI20 relocations that are used to get the address of a specific GOT slot, where I'm not sure an addend is logical:

• R_RISCV_TLS_GOT_HI20 used by TLS IE
• R_RISCV_TLS_GD_HI20 used by TLS GD
• R_RISCV_TLSDESC_HI20 used by TLSDESC

I think none of these should take into account the Addend, as I understand.

I am less sure about R_RISCV_GOT32_PCREL but it could be another one that must have a zero addend.

[aswaterman]

Given #188, this makes sense. AFAICS, we should allow addends for TLS LE but not others.

[jrtc27]

Yeah, those should all fall into the same category as GOT_HI20