Hi, I finally had a chance to try this myself on stretch.
Mumble 1.2.x expects C++03, but g++ 6 defaults to C++11/C++14 (not sure which). We (upstream) don't explicitly pass -std=c++03 to g++ -- so we let the compiler choose. I just tested building Mumble with an explicit -std=c++03 flags. That makes it build and link correctly. So I consider that to be the fix. (And we'll add it to an upcoming Mumble 1.2.x release). Now, with that said, since Mumble 1.2.x seems to build just fine in in C++11 (or greater) mode. Just for the record, If I add the c++11 lib dir, it also works in C++11 mode: --- compiler.pri +++ compiler.pri @@ -89,6 +89,8 @@ unix { QMAKE_LFLAGS *= $(shell dpkg-buildflags --get LDFLAGS) QMAKE_CFLAGS *= -Wfatal-errors -fvisibility=hidden QMAKE_CXXFLAGS *= -Wfatal-errors -fvisibility=hidden + QMAKE_CXXFLAGS *= -std=c++11 + QMAKE_LIBDIR = *= /usr/lib/x86_64-linux-gnu/c++11 !CONFIG(quiet-build-log) { QMAKE_CFLAGS *= -Wshadow -Wconversion -Wsign-compare QMAKE_CXXFLAGS *= -Wshadow -Woverloaded-virtual -Wold-style-cast -Wconversion -Wsign-compare But I consider -std=c++03 to the correct fix, since Mumble 1.2.x wasn't written with C++11 or greater in mind.