GitLab

Force libtool to static link the PIC version of our jemalloc import into
libaml, making libaml standalone. This requires us to test some
additional libraries in our own configure (pthread, and dlopen).

This also solves the long-standing issue of `make check` only working after
`make install`, while removing our custom jemalloc from the installed
libraries.

Fixes #26.

Add parallel option to the compile step to speed things up.

Disable CI runs for refs that are work in progress.

Simple gitlab-ci config with a single step, running the full list of
configure, make, make install and make check.

No tags, no split build and test for now, as artifacts are a bit tricky
to get right.

This config should grow in the future to ensure that we run all the test
on all the platforms we want.