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
Rather than having two separate sections with duplicated information
lets just have one for the common settings, and only document sections
specific to each file in separately
This allows the person running configure (either a developer, user, or
distro maintainer) to keep a configuration of where various kinds of
files should end up.