if nobody fixed build (let alone run) in 6 months, they are de facto
unmaintained.

also move emscripten-fastcomp since it is only used for emscripten
according to APKBUILD comments.

roughly based on this script:

git checkout v3.13.0
grep -l 'arch=""' */*/APKBUILD > 3.13
git checkout master
grep -l 'arch=""' */*/APKBUILD > master
comm -12 3.13 master | cut -d / -f 1-2 | xargs -I{} git mv {} unmaintained/

closes #10402, #10995.