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
Without this, files() in the arguments give an error because it's a list
of mesonlib.File objects:
Array as argument 1 contains a non-string.
It also breaks in nested lists. Includes a test for this.
* Use the env variable to $PATH is searched instead of hardcoded
* Enables a local python build to take priority over system python build
as commonly used by tools like virtualenv.