Fix for mangling problems when using objc++ (.mm) files

Test case:
1. Create example project
2. Change one of the files (that imports cocos3d) from .m to .mm extension - project compiles without issues
3. Add following example code to any of the methods in .mm file:
```
    // Objective C++ test
    CC3Vector4 v = CC3RayIntersectionWithPlane(CC3RayMake(0, 0, 0, 0, 0, 0), CC3PlaneMake(0, 0, 0, 0));
```
4. Try to compile project
5. Linker gives error:
```
Undefined symbols for architecture <used_arch>:
  "CC3RayIntersectionWithPlane(CC3Ray, CC3Plane)", referenced from:
      -[ObjCppExampleScene initializeScene] in ObjCppExampleScene.o
ld: symbol(s) not found for architecture <used_arch>
```

This pull request fixes issue for CC3Foundation header, but similar changes might be needed for other files.