At minimum the Fiber build file should avoid building on platforms it doesn't support. It does that for the tests with the following:

    [ requires cxx11_auto_declarations

               cxx11_constexpr

               cxx11_defaulted_functions

               cxx11_final

               cxx11_hdr_tuple

               cxx11_lambdas

               cxx11_noexcept

               cxx11_nullptr

               cxx11_rvalue_references

               cxx11_template_aliases

               cxx11_variadic_templates  ]

But doesn't do the same for the libs/fiber/build/jamfile.v2. Oliver you should add that requires to the "boost_fiber" lib target.