Update bundled TNG

Update bundled TNG

This commit bundles 6e41191016 from the TNG repo.

Required TNG 1.7.10 in future, which is the first version to include
support for the build system features used here.

Update the build system to use imported targets and interface properties
that TNG now provides.  Add support for building TNG that also bundles
zlib, which reduces the dependency footprint of GROMACS, which is
important for portability and ease of installation.

Refs #1908.

Change-Id: Ibc94d5a9470136331045738f105634ec95fdb455