The problem occurs at this place in configure.ac:

  GST_CHECK_CONFIGPROG(DVDNAV, dvdnav-config)
  if test x"$HAVE_DVDNAV" = x"yes"; then
    dnl check version
    DVDNAV_VERSION=`dvdnav-config --version|head -n 1|sed 's/^.*) //'|sed
's/ (.*)//'`
    DVDNAV_MAJOR=`echo $DVDNAV_VERSION | cut -d. -f1 | sed s/[a-zA-Z\-].*//g`
    DVDNAV_MINOR=`echo $DVDNAV_VERSION | cut -d. -f2 | sed s/[a-zA-Z\-].*//g`
    DVDNAV_MICRO=`echo $DVDNAV_VERSION | cut -d. -f3 | sed s/[a-zA-Z\-].*//g`
    if [[ "$DVDNAV_MAJOR" -eq "0" ]] && \
       [[ "$DVDNAV_MINOR" -lt "1" ]]; then
      AC_MSG_WARN([libdvdnav >= 0.1.7 is required, you have $DVDNAV_VERSION])
      HAVE_DVDNAV="no"
    elif [[ "$DVDNAV_MAJOR" -eq "0" ]] && \
         [[ "$DVDNAV_MINOR" -eq "1" ]] && \
         [[ "$DVDNAV_MICRO" -lt "7" ]]; then
      AC_MSG_WARN([libdvdnav >= 0.1.7 is required, you have $DVDNAV_VERSION])
      HAVE_DVDNAV="no"
      fi
    fi
  AS_SCRUB_INCLUDE(DVDNAV_CFLAGS)

'dvdnav-config --cflags' gets '-I/usr/include/dvdnav',
but AS_SCRUB_INCLUDE promptly scrubs '-I/usr/include' off.