[tlbuild] Support for musl

[Henri Menke]

On Tue, 2018-01-30 at 00:57 +0100, Reinhard Kotucha wrote:
> On 2018-01-30 at 12:12:54 +1300, Henri wrote:
> 
>  > My patch for config.guess was accepted.
> 
> Congratulations!
> 
>  > It uses ldd to detect whether musl is used because ldd prints "musl
>  > libc" to stderr.
> 
> What does config.guess return?

$ sudo docker run --rm -v `pwd`:/config -w /config -it alpine
/config # ./config.guess
x86_64-pc-linux-musl

> 
> Regards,
>   Reinhard
>