==================
WARNING: ThreadSanitizer: data race (pid=74663)
  Write of size 8 at 0x0000025a2ec8 by main thread (mutexes: write M683):
    #0 MxSetMusicSource(void (*)(short*, unsigned long)) <null> (openttd+0x119c1c9)
    #1 MusicDriver_FluidSynth::Start(std::vector<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > const&) <null> (openttd+0xcd8ff7)
    #2 DriverFactoryBase::SelectDriverImpl(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, Driver::Type) <null> (openttd+0x1032b18)
    #3 DriverFactoryBase::SelectDriver(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, Driver::Type) <null> (openttd+0x10327f4)
    #4 openttd_main(int, char**) <null> (openttd+0x12cc060)
    #5 main <null> (openttd+0xd93a42)

  Previous read of size 8 at 0x0000025a2ec8 by thread T2 (mutexes: write M636):
    #0 MxMixSamples(void*, unsigned int) <null> (openttd+0x119af62)
    #1 fill_sound_buffer(void*, unsigned char*, int) <null> (openttd+0xf49856)
    #2 <null> <null> (libSDL2-2.0.so.0+0x2556e)

  Location is global '_music_stream' of size 8 at 0x0000025a2ec8 (openttd+0x0000025a2ec8)

  Mutex M683 (0x00000243d4c0) created at:
    #0 pthread_mutex_lock <null> (openttd+0xa052e6)
    #1 __gthread_mutex_lock(pthread_mutex_t*) <null> (openttd+0xc9f296)
    #2 std::mutex::lock() <null> (openttd+0xca7ca8)
    #3 std::lock_guard<std::mutex>::lock_guard(std::mutex&) <null> (openttd+0xca72d2)
    #4 MusicDriver_FluidSynth::Start(std::vector<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > const&) <null> (openttd+0xcd8eec)
    #5 DriverFactoryBase::SelectDriverImpl(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, Driver::Type) <null> (openttd+0x1032b18)
    #6 DriverFactoryBase::SelectDriver(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, Driver::Type) <null> (openttd+0x10327f4)
    #7 openttd_main(int, char**) <null> (openttd+0x12cc060)
    #8 main <null> (openttd+0xd93a42)

  Mutex M636 (0x7b0c00007170) created at:
    #0 pthread_mutex_init <null> (openttd+0x9e949d)
    #1 <null> <null> (libSDL2-2.0.so.0+0xee6e6)
    #2 DriverFactoryBase::SelectDriverImpl(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, Driver::Type) <null> (openttd+0x1032b18)
    #3 DriverFactoryBase::SelectDriver(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, Driver::Type) <null> (openttd+0x10327f4)
    #4 openttd_main(int, char**) <null> (openttd+0x12cc00b)
    #5 main <null> (openttd+0xd93a42)

  Thread T2 'SDLAudioP2' (tid=74669, running) created by main thread at:
    #0 pthread_create <null> (openttd+0x9e7f1b)
    #1 <null> <null> (libSDL2-2.0.so.0+0xee1ba)
    #2 DriverFactoryBase::SelectDriverImpl(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, Driver::Type) <null> (openttd+0x1032b18)
    #3 DriverFactoryBase::SelectDriver(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, Driver::Type) <null> (openttd+0x10327f4)
    #4 openttd_main(int, char**) <null> (openttd+0x12cc00b)
    #5 main <null> (openttd+0xd93a42)

SUMMARY: ThreadSanitizer: data race (/media/ceeac/Projects/code/openttd/build/openttd+0x119c1c9) in MxSetMusicSource(void (*)(short*, unsigned long))
==================

cmake -DCMAKE_C_COMPILER=clang-10 -DCMAKE_CXX_COMPILER=clang++-10 -DCMAKE_CXX_FLAGS="-fsanitize=thread" -DCMAKE_EXE_LINKER_FLAGS="-fsanitize=thread" ..