Check zlib can actually be linked

Only use zlib compression in tng if zlib can really be linked.
This is equivalent to ee26e1264 for libxml2.

It is slightly simpler than the approach in gmxTestLibXml2
and CheckLibraryExists could be used there too.
This does not detect potential linking errors with shared
libraries similar to those solved in #740 for FFTW.

Fixes #1435

Change-Id: I5009e50b6caf810a12e71ecd83bde2edb21a2b32