FWIW, the "overflow in constant expression [-fpermissive]" errors may be a compiler bug, see: https://gcc.gnu.org/ml/gcc-bugs/2016-02/msg00303.html
- Bug#811998: gamera: FTBFS with GCC 6: misc errors Daniel Stender
- Bug#811998: gamera: FTBFS with GCC 6: misc error... gamera@discard.email
- Bug#811998: gamera: FTBFS with GCC 6: misc e... Daniel Stender
- Bug#811998: gamera: FTBFS with GCC 6: mi... Jakub Wilk
- Bug#811998: gamera: FTBFS with GCC 6... Daniel Stender