We currently build the LibC++ libraries with an alternative build system, mainly because historically it was not possible to build the library for a cross-compiler. That of course is getting better with the wholesale move over to CMake.
At the moment we build the library with ‘-std=c++11’. This seems to produce a library that is valid for linking with programs compiled for C++98 and C++11, and very few people seem to be compiling their code with C++14. We have no had reports of problems.
But should I really be building 3 versions of the library, one each for C++98, 11 and 14? Or will a C++14 built library be link compatible for all the earlier dialects?