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
If a configure_file has an install_dir set, the supported install
argument is ignored, while this should have actually higher priority
than the install_dir itself.
Also check that correct types are used for `install` and `install_dir`.
Add test to verify this.
Fixes#3983