Add Meson build system and Gitlab-CI
This expands on @wjt's MR !5 (closed) with my suggested fixes for test failures, and also a commit to make the build succeed without warnings on archaic gcc versions (gcc 4.8, which by default doesn't compile in C99 mode and issues warnings about G_STATIC_ASSERT
).
/cc @wjt
Edited by Simon McVittie