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
At the same time, this also adds a bunch of tests that document and keep
track of how we expect quoting to pass through via Ninja to the
compiler.
We need at least Ninja 1.6.0 for this.
This fixes https://github.com/mesonbuild/meson/issues/489