Add support for musl-libc on Linux

[Rafael Espíndola via llvm-commits]

On 13 June 2016 at 09:25, Lei Zhang <zhanglei.april at gmail.com> wrote:
> 2016-06-13 21:02 GMT+08:00 Rafael Espíndola <rafael.espindola at gmail.com>:
>> Should musl really be an environment? What happens when targeting ARM,
>> do we get a gnueabi+musl? Is it used as an environment when
>> configuring gcc?
>
> Honestly I couldn't judge if musl *should* be an environment. But it
> *is* used as an environment when configuring gcc, and
> "x86_64-pc-linux-musl" could be parsed by config.sub as a valid
> triplet.
>
> As for ARM, I guess something like arm-linux-musleabi would do.


OK, it is slightly annoying that we will have a Foo and FooMusl
environments, but if that is what is used for configuring gnu tools I
think it is the correct thing for us to do.

So the patch LGTM. We can extend it to handle other architectures once it is in.

Cheers,
Rafael