Kris pointed me to:
xgobi builds on 4-stable but not on 5.1-CURRENT #3: Mon Nov 17
I am not familiar with details of Imakefiles but it
looks like imake or more likely one of the tools imake calls
has changed (cpp?) and comments are handled differently.
Patch to change all comments to use standard C type delimiters.
o Some whitespace changes in comments due to new format.
o Changed one comment due to it referencing a following line
which has moved down two more lines due to te commenting whitespace
Tested on 4.9-RC #6: Sat Oct 4 as well as 5.1-CURRENT #3: Mon Nov 17.
I have not contacted authors regarding this issue, since during my last
discussion (over 12 months ago) they inidcated that xgobi was not
going to be maintained as they were working on a replacement package.