Use default C++11 support in recent clang
Use default C++11 support in recent clang

Just as for modern gcc, modern clang (clang 6 or later)
uses C++14 (or later) by default, so no explicit -std=c++11
flag is needed (and may in fact be harmful).

salilab/rmf,salilab/rmf,salilab/rmf,salilab/rmf