This is supposed to be some C++17 thing.
g++ takes this in c++1z, c++14, c++11, ...
Hmmm.
Add constexpr_complex.cpp to test failure of constexpr unary -.
This is sad.
Try to make dynarray statis-only by forbidding heap allocation.
Explicit new fails.
For some reason vector still works - placement newneeds clobbering?