Yes, it's possible to build the portable version 7.3 under any system because macOS support was removed from portable version for security reasons.
Note that if you want to generate the Windows executable files and don't have a signature, you should run windowsSignedPortableLaunchers target after removing the lines 1547 to 1563 in build.xml.
Then, you have to fill the [font=courier new]runtime[/font] folder with JREs (you can copy them from exisitng portable version), and fill the subdolders of [font=courier new]data[/font] with the libraries of your choice. These folders are empty when you run the current portableArchive target.