ldas-tools-framecpp doesn't build on arm64 architecture

I seem to have misplaced the report at https://git.ligo.org/ed-maros/LDAS_Tools/issues/3 but would like it to be considered for an upcoming release - apparently it's got to do with a "-m64" option and has been present since 2.6.3 (2.6.2 was the last version that build successfully).