auto-multiple-choice/auto-multiple-choice-devel: fix build failures for older macOS releases, or set known_fail

[mascguy (Christopher Nielsen)]

Presently these two ports are failing to build for older macOS releases, causing a significant amount of wasted time on the buildbots. (Note that the port itself builds quickly. Instead, it's the installation of dependencies which takes the bulk of the time.)

However, this might be easily fixable, perhaps with an appropriate compiler blacklist.

Here's one example, for 10.7:

​https://build.macports.org/builders/ports-10.7_x86_64-builder/builds/72714/steps/install-port/logs/stdio

gcc -o AMC-buildpdf AMC-buildpdf.cc  -O2 -I/opt/local/include -I. -DNEEDS_GETLINE -std=c++11 -L/opt/local/lib   -lstdc++ -lm -I/opt/local/include/pango-1.0 -I/opt/local/include/harfbuzz -I/opt/local/include/pango-1.0 -I/opt/local/include/fribidi -I/opt/local/include/harfbuzz -I/opt/local/include/poppler/glib -I/opt/local/include/poppler -I/opt/local/include/cairo -I/opt/local/include/glib-2.0 -I/opt/local/lib/glib-2.0/include -I/opt/local/include/pixman-1 -I/opt/local/include/ossp -I/opt/local/include/freetype2 -I/opt/local/include/libpng16 -L/opt/local/lib -lpangocairo-1.0 -lpango-1.0 -lharfbuzz -lpoppler-glib -lgobject-2.0 -lglib-2.0 -lintl -lcairo -I/opt/local/include/opencv4 -L/opt/local/lib/opencv4 -lopencv_gapi.4.5.0 -lopencv_highgui.4.5.0 -lopencv_ml.4.5.0 -lopencv_objdetect.4.5.0 -lopencv_photo.4.5.0 -lopencv_stitching.4.5.0 -lopencv_video.4.5.0 -lopencv_calib3d.4.5.0 -lopencv_features2d.4.5.0 -lopencv_flann.4.5.0 -lopencv_videoio.4.5.0 -lopencv_imgcodecs.4.5.0 -lopencv_imgproc.4.5.0 -lopencv_core.4.5.0

cc1plus: error: unrecognized command line option "-std=c++11"cc1plus: error: unrecognized command line option "-std=c++11"

But if the blacklist option doesn't work, we should set known_fail for older releases, and save previous buildbot time.