libicu-le-hb.0.dylib: undefined symbol: _ZTIN6icu_657UObjectE

[Chris Jones]

> BTW, what are the effects of setting `compiler.cxx_standard 2011`? Does it just set a minimal compiler version or does it also add a `-std=` flag somewhere?

It just ensures a compiler capable of the require standard is used. It 
does not append any compiler flags, that is up to the port / build 
system (e.g. a specific build might want gnu++11 instead of c++11, etc.).