The build system already detects if GCC 6 is being used and applies required tweaks need for the build process to complete. Note that it is not recommended to use GCC 6 and your mileage may vary on stability of the resulting binary.
Thanks for the info. It's possible on Stretch to tell it to use gcc-5 instead, since that seems to be working on Ubuntu 16.10.
Since the same source packages are building correctly on 16.10, I added the repository to the others instead of having a separate one, which I'll soon delete.
I also searched around the OBS for other palemoon packages; this one for 26.5.0 on openSUSE was successful.https://build.opensuse.org/package/show ... p/palemoon
since I know nothing about rpm packaging nor run that type of distro, I don't know whether these source files can be used for other rpm type distros offered by the OBS, such as Centos 5, 6, 7 or Redhat.