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
The documentation already contains an example for PCH but misses the
to show the content of the PCH files and how to create them.
With this commit exactly this is exlained.
This allows us to more easily have the documentation in sync with
the source code as people will have to document new features etc
right at the time where they implement it.