Build breaks with GCC >= 6.5 and libboost 1.58 in Ubuntu 16.04

As shown in the log for Job #2007 (b9d1ae5f), building with --enable-tests causes linker errors. The reason is that in boost 1.58, several functions in boost::regex don't have a C++11-compliant ABI.

boost::re_detail::cpp_regex_traits_implementation<char>::transform_primary[abi:cxx11](char const*, char const*) const
boost::re_detail::cpp_regex_traits_implementation<char>::transform[abi:cxx11](char const*, char const*) const