maint: Add encoding marker for Emacs to non-ASCII sources. Similar to commit f406941a8a2ec5fbf3eacc386b9be09d6593d53b from Paul Eggert <eggert@cs.ucla.edu> 2015-09-24. To determine the file list that need the marker, I used the command: for f in `find . -type f | grep -v '^\./\.git/' | grep -v '^\./tests/'`; do if iconv -f ASCII -t ASCII < $f > /dev/null 2>&1 ; then : ; else if iconv -f UTF-8 -t UTF-8 < $f > /dev/null 2>&1 ; then if grep 'The GNU C Library is' $f > /dev/null; then :; else if grep 'coding: utf-8' $f > /dev/null; then :; else echo $f fi fi fi fi done | LC_ALL=C sort