Add debug information to Windows builds
Add debug information to Windows builds

Previously, Windows builds were being produced without debug
information, leading to somewhat unhelpful backtraces etc.
without symbols.

This builds the symbols in (only for debug builds - I've
deliberately not touched release builds here) so gdextension
bugs are a little more tractable.

Test-Information:
Have been running this patch for weeks, and getting useful
traces out on the commandline, and useful debugging from
debuggers.

godotengine/godot-cpp,godotengine/godot-cpp,godotengine/godot-cpp,godotengine/godot-cpp