Unfortunately the GCC compiler does not emit enough information about defines to parse them during debugging. However, VisualGDB has a separate mechanism of tracking peripheral register names and replacing them with the corresponding expressions in the Watch window. If your register is not recognized, you can try editing the device definition files in %LOCALAPPDATA%VisualGDBEmbeddedBSPsarm-eabicom.sysprogs.arm.stm32devices (you can unzip the xml.gz file and just keep the .xml one, VisualGDB will use it automatically).