One can now set the variable OPM_BINARY_PACKAGE_VERSION to a
meaningful version string (Debian 11.2: 2021.10-4). When building
outside of git it will be used as the project hash. If the variable is
non-empty there will also be no timestamp in project-timestamp.hh (as
this would break reproducible builds).
Note that if building from git or not setting the variable then everything
will be like before.
The changes are:
- Add new macros PROJECT_VERSION_NAME and PROJECT_VERSION_HASH
in addition to the existing PROJECT_VERSION.
- Add header include guards.
