It seems like it is not clear from the docs when this was turned on by default, so not clear if one should bump the version or possibly clarify how to build with 4.8.1? That is, how to pass the compiler flag (environment variable?).

https://gcc.gnu.org/projects/cxx-status.html#cxx11 says 4.8.1 is the minimum that implements c++11 and 6.5 (https://gcc.gnu.org/onlinedocs/gcc-6.5.0/gcc/Standards.html#C_002b_002b-Language) is the first version that defaults to c++11 (well, actually gnu++14 which I am assuming is a superset of c++11).

I think the lazy fix here is to add a note that for old gcc the CXXFLAGS env needs to be set, the better fix (which I do not know the right place to do!) is to detect and add this flag as part of the build chain.

IMHO lazy is good enough here. If somebody is able and wiling enough to compile from source, we can expect them to read the docs (at least when something is not working). Also this will become less important one time less because it only affects older gcc versions. Both reasons make the issue less critical.