[tlbuild] Support for musl

[Norbert Preining]

> You can obtain the updated .travis.yml from my GitHub:
> https://github.com/hmenke/texlive-source/blob/master/.travis.yml

Thanks, I will look into it.

> Native Travis (a.k.a. Ubuntu 14.04 amd64)
> Debian amd64
> Debian i386

These are not needed as we build them on even older systems to get the
oldest libc possible (with the new C++ requirement this is getting
difficult, though).

> Alpine x86_64
> Alpine x86

The would be uploaded to the tug server and made available for
custom-bin installation.

> The Debian and Alpine builds run via Docker and generate a tar.gz archive which contains the "inst"

Actually inst/bin/* only. We also should decide on a naming how to put
them on the web. Probably
  i386-linux-musl
  x86_64-linux-musl
is fine. 

> directory.  The Alpine x86 build does not work though and hangs indefinitely which I can also
> https://travis-ci.org/hmenke/texlive-source/jobs/333045568

This is indeed strange an error:
  checking for pkg-config... (cached) pkg-config
  checking that generated files are newer than configure...
  No output has been received in the last 10m0s, this potentially indicates a stalled build or something wrong with the build itself.

More when I have some spare time ...

Norbert

--
PREINING Norbert                               http://www.preining.info
Accelia Inc.     +    JAIST     +    TeX Live     +    Debian Developer
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