binutils-2_28-branch, master: Don't use "_gp" on RISC-V, use "_global_pointer$" instead

[Tristan Gingold]

> On 10 Feb 2017, at 03:12, Palmer Dabbelt <palmer@dabbelt.com> wrote:
> 
> This was one of the things Andrew and I found during our pre-upstreaming code
> review, but we forgot about it.  I was recently cleaning up the bugs in our
> Github bug tracker and found it, and I thought it would be worth proposing a
> fix here.
> 
> The issue is that we use the "_gp" symbol to store the global pointer, which
> can conflict with ABI-complient code on RISC-V (it's not in any namespace or
> anything).  This was copied from MIPS, so hopefully it's not going to break
> real programs, but we thought that we should try and fix it while we still can.
> 
> This will break the RISC-V ABI, but my understanding is that is still OK
> because we haven't released yet.  That means we _need_ to get this on the 2.28
> branch if it lands on master, which is why I've added Tristan Gingold and the
> binutils-2_28-branch tag even though this hasn't made it to master yet.
> 
> This patch passes all my test cases, and Andrew and I approve of it.  I'm
> mostly wondering if this is still OK to change in our port, and if it's OK for
> 2.28.

That's ok for 2.28 once in the trunk.

Tristan.