There are two implementations of the standard C++ library available on OS X: libstdc++ and libc++. They are not binary compatible and libMLi3 requires libstdc++.
On 10.8 and earlier libstdc++ is chosen by default, on 10.9 libc++ is chosen by default. To ensure compatibility with whatever fails, we need to choose libstdc++ manually.
To do this, add -stdlib=lib(std)c++ to the linking command.
Could you try adding those two lines to your .pro File?
QMAKE_CXXFLAGS += -std=c++11
QMAKE_CXXFLAGS += -stdlib=libc++
if this doesnt work try
QMAKE_CXXFLAGS += -std=c++11
QMAKE_CXXFLAGS += -stdlib=libstdc++
Always clean and rerun qmake before compiling.
doesn't work...