I have found the solution. The problem is with Xcode's version of Clang. Mt32emu-qt compiled once I specified the compilers to /usr/bin/gcc and /usr/bin/g++ in CMake. That should be a temporary solution until/if Apple fixes the bug in its version of Clang.
Funnily as you are on Lion and thus on Xcode 4.2 or 4.3x you don't actually have gcc 😉 those gcc & g++ in usr/bin are just symlinks to lvm-gcc/g++
I've run into something like that too before some time ago. You could send Apple a bug report if you are in thd developer program.
I've tried to compile this in Linux. The cmake step failed because it couldn't find PulseAudio. I deleted that from the CMakeLists.txt.
Aftet that, the build aborted because it couldn't find "asoundlib.h". I've fixed mt32emu_qt/src/audiodrv/AlsaAudioDriver.h to #include <alsa/asoundlib.h> instead.
That worked and I got a binary. I ran it, but when I select "Options->ROM Configuration", it crashes with:
1Qt has caught an exception thrown from an event handler. Throwing 2exceptions from an event handler is not supported in Qt. You must 3reimplement QApplication::notify() and catch all exceptions there. 4 5terminate called after throwing an instance of 'std::bad_alloc' 6 what(): std::bad_alloc 7Aborted