This is a very rudimentary version. All it does is copy and rename the
template header file and place it in the build directory in a special
subdirectory that is added as an #include-path.

There is some code duplication and cleanup necessary. There are a
few "magic strings" and "magic paths" that need to be removed as well.

Remove `-lstdc++fs` from the default link flags

Fix for Clang not working with MacOS

On MacOS and (I think) most BSDs the default standard library is libc++, and so attempting to link with libstdc++fs does not work.

On Linux, where (AFAIK) most distros use Clang/libstdc++, this is going to mean link-time failures when using std::filesystem. In this case the user can add Link-Flags: -lstdc++fs to their toolchain file themselves as a fix.

This is intended to fix #11.

Unfortunately I haven't been able to successfully build DDS yet to actually try it out, but looking at the surrounding code it seems like the right solution...