This is a) useless because it's only used to print which options are not
default, and b) harmful because it can result in cases where things
break, like in projects that set a standard that the chosen compiler
doesn't support, but the project (or some subset) can be built with a
different standard.
Fixes: #8360
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
Add a test that trying to use a native compiler in a target after it's
been tentatively added with add_languages() without native: but isn't
actually available gives an error.