Core/Buildsystem: Add a warning about missing git revision info during CMake configuration:

This will trigger when the rev_hash has not been set properly, and inform of possible steps to take (in most cases pulling repository tags is sufficient)

cmake/genrev.cmake

@@ -52,6 +52,9 @@ endif()
 # If everything above fails (means the user has erased the git revision control directory or removed the origin/HEAD tag)
 if(NOT rev_info)
   # No valid ways available to find/set the revision/hash, so let's force some defaults
+  message("")
+  message(STATUS "WARNING - Missing repository tags - you may need to pull tags with git fetch -t")
+  message(STATUS "WARNING - Continuing, but the hash will be set to 'Archive'")
   set(rev_hash_str "Archive")
   set(rev_hash "0")
 else()