https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63622
--- Comment #15 from Jonathan Wakely <redi at gcc dot gnu.org> --- (In reply to howarth from comment #14) > which produces as set of warnings that don't appear in the build of > libstdc++-v3/src/c++98/streambuf-inst.cc. These are... > > ./../../../../gcc-5.0-20141105/libstdc++-v3/src/c++11/streambuf-inst.cc:63:1: > warning: alias definitions not supported in Mach-O; ignored I have no idea what that means or why building the file with -std=c++11 instead of -std=c++98 causes it, and I don't have any way to check what is different on darwin.