>Also, those flags are specific to C++ compiler command. They cannot be reliably used as CXXFLAGS or LDFLAGS, especially LDFLAGS is shared among different compilers/linker and may cause problem (e.g., building open-mpi when gfortran is in use). So adding those flags to $CXX is the only reliable way to specify C++11 mode, which I think is safe here.

Well, the cc wrapper is pretty fine-grained so it should be pretty easy to only add them at the appropriate times. Currently it doesn't differentiate between being invoked as `cc` or `cxx` (until it actually exec's the correct tool) but it would be trivial to add `:cxx` as a mode.