D lang compilers have an option -release (or similar) which turns off
asserts, contracts, and other runtime type checking. This patch wires
that up to the b_ndebug flag.
Fixes#7082
This can be useful to make sure that a project builds when
its fallbacks are used on systems where external dependencies
satisfy the version requirements, or to easily hack on the sources
of a dependency for which a fallback exists.
Deprecated Meson syntax is not supported.
There are features not yet implemented, like completing
build targets and build options; more on this in the comments.