gcc-16, first packaging bits

gcc-16 is now packaged as a first attempt, please see

  deb https://people.debian.org/~doko/tmp/gcc-16 ./

Not uploading for experimental, because there are still some foreseeable 
soname bumps for various runtime libraries.

As long as this is not yet in the archive, please report bugs under the 
gcc-snapshot package.

For a little more architecture support, please also see the package in
https://launchpad.net/~ubuntu-toolchain-r/+archive/ubuntu/test

Matthias