[tlbuild] Support for musl

[Henri]

On Fri, 2018-01-26 at 10:04 +0900, Norbert Preining wrote:
> Hi all,
> 
> > 
> > x86_64-alpine-linux-musl
> That is not really a triplet but quadruplet, right? Why does Alpine
> Linux inject their name here? Quite strange I think.

You're right it's strange.  The triplet is

    machine-vendor-operatingsystem

and in this case

    machine = x86_64
    vendor = alpine
    operatingsystem = linux-musl

Sometimes vendor is just unset.  Unfortunately someone had the glorious idea to
use dashes in the operatingsystem string as well which makes it really
ambiguous.  The wiki article I linked in the last mail has more info about that
https://wiki.osdev.org/Target_Triplet

---

On another notice, I managed to successfully build with Alpine i386 on Travis by
downgrading to a much earlier version (3.1 released in Dec 2014, support ended
Nov 2016).  The problem of hanging builds on the most recent 3.7 persists
though.

Also Debian is downgraded to 8 (jessie).  Debian 7 (whezzy) ships too old GCC
for C++11.

I updated my .travis.yml with those changes.

> 
> > 
> > > 
> > > I don't have any specific reason, but on the other hand, I don't want to
> > > go to three part names unless there is a clear need. (This is the reason
> > > I asked Mojca to use the two-part x86_64-darwinlegacy when that started
> > > up.)
> In case we ever switch, TLUtils::platform_name as well as some other
> function would need to be carefully checked!
> So I am also in favor of keeping $CPU-$OSPLUS layout.
> 
> Best
> 
> Norbert
> 
> --
> PREINING Norbert                               http://www.preining.info
> Accelia Inc.     +    JAIST     +    TeX Live     +    Debian Developer
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