Bug#1076436: highway: Add autopkgtest.

[Jeremy Bícha]

I'm not the Debian maintainer for highway, but here's a suggestion:

-Depends: @, g++
+Depends: libhwy-dev, g++

since the point of this is to test that libhwy-dev works and has its
Depends set correctly.

I have uploaded your patch with my suggested change to Ubuntu since we
need an autopkgtest like this there for Ubuntu main inclusion
processes.

https://launchpad.net/ubuntu/+source/highway/1.2.0-3ubuntu1

Thank you,
Jeremy Bícha