After investigating further, I found the problematic package to be mesa-opencl-icd.
After removing the package above, gimp works again.
- Bug#964810: gimp: Failure to start - GTK proble... Nikolai Lusan
- Bug#964810: gimp: Unable to start gimp in ... zeden
- Bug#964810: gimp: Unable to start gimp... felipe
- Bug#964810: gimp: Unable to start ... Simon McVittie
- Processed (with 2 errors): Re: Bug#964810:... Debian Bug Tracking System
