Do not cache version in cmake build
Summary: The cmake build produce stale version numbers as a result of the caching.
Build with cmake.
Increment the version number of bitcoin-abc in /CMakeLists.txt .
Rebuild, make sure the version actually changed in the generated version.h
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D4228