Fix RISC-V CFA relocations

[Palmer Dabbelt]

On Mon, 13 Mar 2017 14:47:50 PDT (-0700), Palmer Dabbelt wrote:
> Without this patch set we don't correctly compute CFA relocation offsets, which
> means debug info is broken on RISC-V.
>
> [PATCH 1/3] Fix the offset of CFA relocation.
> [PATCH 2/3] Fix DW_CFA_advance_loc relocation.
> [PATCH 3/3] Define DWARF2_USE_FIXED_ADVANCE_PC.

Committed.