There are C++11 constructs in Icarus at the moment and the plan is to
retain C++11 compatibility until more modern versions are widely available
in the default installation of systems.
Pass `-std=c++11` to the compile to enforce building with C++11, this will
make sure that neither an older nor a newer version is used. E.g. compilers
on some platforms still default to an earlier version of C++11.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>