Xcode 8.3.1 - Update causing unusual errors in C++ code?

Edit:

I have been developing a C++ application for a while now, and I have been able to run it perfectly up until the day after Xcode auto updated to 8.3.1. Since then, after trying to build my code, I get all sorts of weird errors that don't make any sense. Such as:

class Renderable2D : public Object { ... }
                           ^

It says that it "Expected class name" where Object is a class I have defined.

void render(Renderer2D* renderer) const override;
                                       ^

It says that "Only virtual member functions can be marked 'override'" when in fact that method was virtual!

And there are a ton more errors where that came from! (12 to be exact!)

I have been tearing my hear out to try and figure out what caused these issues and haven't been able to come up with an explanation other than the update, so I tried downloading Xcode 8.3 to replace the new updated one, but even on that these errors come back!

Any help would be greatly appreciated!

Any chance that the file(s) in question are not actually being processed by the C++ compiler?

(If you check the individual compile commands as echoed into the Report Navigator, it should tell you the details.)

All of those files are processed by the C++ compiler (LLVM.)