This is like the project options, but for meson builtin options.
The only real differences here have to do with the differences between
meson builtin options and project options. Some meson options can be set
on a per-machine basis (build.pkg_config_path vs pkg_config_path) others
can be set on a per-subproject basis, but should inherit the parent
setting.
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