Generating revision during build can silently fail

For some reason (unknown atm) in one of testing environments successfull build didn't generate correct git_version.hpp header (empty one has been created). That caused other failures in consequence (i.e. at installation).

We should try to enforce an EXECUTE_PROCESS used during cmake execution to fail when underlying git spawn fail.

See https://gitlab.syncad.com/hive/haf/-/blob/develop/cmake/git.cmake#L6

Probably storing an exit code by specifying RESULT_VARIABLE property should allow to fix this problem.