Speed up or avoid bootstrap in CI runners
This is just an idea... we have to test it yet.
In the CI images, we could manually run the 3 invocations of gnulib-tool to create gl/, lib/unistring/ and src/gl/. We can even build the gnulib libraries in there and run the gnulib tests.
In the CI runners, we have to cp -a those directories into the gnutls/ directory. Then we create ./configure with autoreconf -fi and go on as normal. [We can possibly even avoid this last step as long configure is newer than configure.ac].
The gain is at least that we avoid ./bootstrap. Still the question, how much weights the 1.x minutes of bootstrapping against the 1,5h of running a pipeline ?