caffe: undefined reference to boost::gregorian::greg_month::as_short_string() const

the reason is due to the missing dependencies of boost date_time library in cmake configuration

Goto root > cmake > Dependencies.cmake

search a keyword: filesystem (original source)
find_package(Boost 1.61 COMPONENTS "python${PYTHON_VERSION_MAJOR}" system thread filesystem regex)

adding a keyword named as date_time into all corresponding search result (modified source):-
 find_package(Boost 1.61 COMPONENTS "python${PYTHON_VERSION_MAJOR}" date_time system thread filesystem regex)