MFH: r499231

graphics/magnum-examples: Mark LLD_UNSAFE and unbreak on FreeBSD 12.0/amd64

/usr/bin/ld: error: cannot preempt symbol: alGenBuffers

defined in /usr/local/lib/libopenal.so
referenced by AudioExample.cpp

src/audio/CMakeFiles/magnum-audio.dir/AudioExample.cpp.o:(Magnum::Examples::AudioExample::AudioExample(Magnum::Platform::Sdl2Application::Arguments const&))

http://beefy6.nyi.freebsd.org/data/120amd64-default/499067/logs/errors/magnum-examples-2019.01.log

PR: 226980

Approved by: ports-secteam blanket