Cycles: Disable OpenCL on macOS

This is unfortunate, but the number of bugs in this configuration
keeps growing, and almost all of them are caused by bug in OpenCL
compiler.

The compiler is not likely to be fixed, since Apple declared OpenCL
deprecated.

This evil commit is aimed to keep officially supported features
of Blender in a good working and stable state.

intern/cycles/device/opencl/opencl_util.cpp

@@ -645,7 +645,7 @@ bool OpenCLInfo::device_supported(const string& platform_name,
 		return true;
 	}
 	if(platform_name == "Apple" && device_type == CL_DEVICE_TYPE_GPU) {
-		return true;
+		return false;
 	}
 	return false;
 }