update cxxtools and tntnet to current (more recent) github releases

[heitbaum]

Both cxxtools and tntnet are the previous releases and the prevous hosting site is now offline.

The giuthub repositiories are at

• https://github.com/maekitalo/cxxtools
• https://github.com/maekitalo/tntnet

There are a number of patches that are now incoporated in upstream - but there is work required to get the build working correctly in our environment (libtool/cross/...)

Ref: d19f4ac