Clang: Don't overwrite c++11 compile option value with c++14 flag.
Clang: Enable c++14 dialect flag with Clang 3.5.
Merge topic 'clang-compile-options-cxx14' into next

49b8140e Clang: Enable c++14 dialect flag with Clang 3.5.
0b80fc35 Clang: Don't overwrite c++11 compile option value with c++14 flag.