betterC DLL in Windows

[Richard (Rikki) Andrew Cattermole]

You don't have access to druntime/Phobos stuff at runtime.

SimpleDllMain is for initializing and uninitializing druntime.

See: 
https://github.com/Project-Sidero/basic_memory/blob/main/source/sidero/base/dllmain.d

You want to only use ldc atm. The defaults right now should most likely 
"just work" in dub for a single compile + link step (i.e. only a single 
static library in dll).

If you do it manually, you'll want to add the flag 
``--fvisibility=public`` to export everything.