adapt code to clang39 --std=c++1z
clang39 with -std=c++1z declares __cplusplus > 201402L, but is not entirely C++17 compliant... so avoid (for now) a pure C++17 construct which was protected by __cplusplus > 201402L...
Edited by Gerhard Raven
clang39 with -std=c++1z declares __cplusplus > 201402L, but is not entirely C++17 compliant... so avoid (for now) a pure C++17 construct which was protected by __cplusplus > 201402L...