I need to set
Finally I've figured it out.
Achieved result: _64BIT macro would be added during preprocessing to every (at least known for today) 64-bit environment, regardless of is it a simulator of 64-bit device or a real 64-bit device.
The solution is to manually edit .pbxproj-file as follows:
GCC_PREPROCESSOR_DEFINITIONS = ( "DEBUG=1", "$(inherited)", ); "GCC_PREPROCESSOR_DEFINITIONS[arch=arm64]" = ( "$(inherited)", _64BIT, ); "GCC_PREPROCESSOR_DEFINITIONS[arch=x86_64]" = ( "$(inherited)", _64BIT, );
So here is debug-config:
Then changes that you've done manually would be visible within Preprocessor settings editor. It really looks like bug in Xcode in the editor.
You can notice that I've already tried this approach before posting the question, but I've misinterpreted the results of my attempt. The thing is that I've tested my app on the simulator, and architectures are different on real device and corresponding simulator. I've configured macro to be included on arm64 architecture, but simulator's actual architecture was x86_64.
For further reference, this article explains where does every architecture actually take place:
For i386 and x86_64 "bitness" of simulated device is implied here, not your Mac's.