-------------
You need to compile using gmake - regular make only appears to work, but doesn't in fact. Use gmake, not make.
-The clang compiler installed through FreeBSD's package manager does not expose all of the C++17 features needed under `std=gnuc++11`. Force the compiler to use `std=c++17` mode instead.
+The clang compiler installed through FreeBSD's package manager does not expose all of the C++17 features needed under the default `std=gnuc++14`. Force the compiler to use `std=c++17` mode instead.
```sh
export CXXFLAGS=-std=c++17