I have compiled gnucash on my sparc workstation, and it seems to work well. I think the ~sparc keyword can be added. The ebuild I used is gnucash-1.8.8.ebuild, located in /usr/portage/app-office/ Reproducible: Always Steps to Reproduce:
*** Bug 47239 has been marked as a duplicate of this bug. ***
Added ~sparc keyword to gnucash and its dependencies. Thanks for the bug report :)