I believe all that's needed is to set required=etags in t/tags-lisp-space.sh. Sorry for my dumb mistake. Committed this:
--- a/t/tags-lisp-space.sh +++ b/t/tags-lisp-space.sh @@ -18,7 +18,7 @@ # if there are CONFIG_HEADERS. # See automake bug#38139. -required='' +required=etags . test-init.sh # some AC_CONFIG_FILES header is needed to trigger the bug.