VSTGUI 4.3 fails compiling on Mac

I am porting some old projects to VSTGUI4. For downward compatibility reasons I am limited to v4.3.
Migrating the project from v3.6 to 4.3 was a huge effort, but it already runs on PC.

The project compiles fine with VSTGUI 3.6 on Mac, but fails compiling with 4.3 on Mac. I get this linker error:

Undefined symbols for architecture x86_64:
OBJC_CLASS$_CALayer”, referenced from:
objc-class-ref in vstgui_mac.o
“_vImagePremultiplyData_ARGB8888”, referenced from:
VSTGUI::CGBitmapPixelAccess::~CGBitmapPixelAccess() in vstgui_mac.o
“_vImageUnpremultiplyData_ARGB8888”, referenced from:
VSTGUI::CGBitmapPixelAccess::CGBitmapPixelAccess(VSTGUI::CGBitmap*, bool) in vstgui_mac.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

It doesn’t seem to be a issue of my project, since the same error appears also for other developers as well es the included tutorial.xcodeproj example.

Here another developer experienced the same:

The same error appears with VSTGUI 4.3.1 and VSTGUI 4.4

Undefined symbols for architecture x86_64:
OBJC_CLASS$_CALayer”, referenced from:
objc-class-ref in vstgui_mac.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

It seems that it’s not even possible to compile the tutorial of any VST4.x GUI…