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 fixes an issue with generated sources and object libraries, as
well as an issue on windows with the `link` linker and the vs backend.
The last issue is resolved by building the source files multiple times
to avoid extracting object files in meson.