binarycreator cannot sign with '-' (adhoc)

While trying to package my cmake project with CPackIFW using an adhoc signature on macOS ARM with CPACK_IFW_PACKAGE_SIGNING_IDENTITY set to "-", I noticed that the binarycreator program cannot accept '--sign -'  as argument because "-" is not detected as a valid value but rather as another command line argument, so an error is sent. However, '-' is a valid value and a useful one. It permits signing .app with an adhoc signature.

This problem can be solved by updating the line below to parse the sign option properly.