While building with gcc6, the build fails with:
[ 300s] Accents.cc:78:42: error: narrowing conversion of '128' from 'int' to 'char' inside { } [-Wnarrowing]
[ 300s] 'o', 'u', 'u', 'u', 'u', 'y', 254, 255};
[ 300s] ^
[ 300s] Accents.cc:78:42: error: narrowing conversion of '129' from 'int' to 'char' inside { } [-Wnarrowing]
[ 300s] Accents.cc:78:42: error: narrowing conversion of '130' from 'int' to 'char' inside { } [-Wnarrowing]
The patch changes from char to unsigned char (which can hold up to int 255
You can get a patch for that. https://packages.debian.org/stretch/htdig
The archive htdig_3.2.0b6-16.debian.tar.xz contains the patches but not the htdig source code.
You could also try hl://Dig, a fork of ht:/Dig that was started almost a year ago.
https://github.com/solbu/hldig