`autopoint` doesn't handle unquoted aux dirs correctly

[awilfox]

Elizafox/tre-regex-sys#1 has led me to a curious thing:

AC_CONFIG_AUX_DIR(utils)

will break gettext-tiny's autopoint:

awilcox on gwyn ~/Code/contrib/tre-regex-sys/tre % find . -name config.rpath
./AC_CONFIG_AUX_DIR(utils)/config.rpath

because it doesn't have the bracket quotes that autopoint is expecting:

  if [ "${line##*AC_CONFIG_AUX_DIR}" != "$line" ]; then
    dirprefix="${line##*([}"
    dirprefix="${dirprefix%%])*}"
    mkdir -p "${dirprefix}"
  fi

Trying to see if we can find an easy fix.