configure: List external libs used using print_enabled()

This cuts some lines from the script as well as the output and
simplifies maintenance.
Signed-off-by: Mans Rullgard <mans@mansr.com>

configure

@@ -3837,40 +3837,14 @@ echo "network support           ${network-no}"
 echo "threading support         ${thread_type-no}"
 echo "safe bitstream reader     ${safe_bitstream_reader-no}"
 echo "SDL support               ${sdl-no}"
-echo "AVISynth enabled          ${avisynth-no}"
-echo "frei0r enabled            ${frei0r-no}"
-echo "gnutls enabled            ${gnutls-no}"
-echo "libcdio support           ${libcdio-no}"
-echo "libdc1394 support         ${libdc1394-no}"
-echo "libfaac enabled           ${libfaac-no}"
-echo "libfdk-aac enabled        ${libfdk_aac-no}"
-echo "libgsm enabled            ${libgsm-no}"
-echo "libilbc enabled           ${libilbc-no}"
-echo "libmp3lame enabled        ${libmp3lame-no}"
-echo "libopencore-amrnb support ${libopencore_amrnb-no}"
-echo "libopencore-amrwb support ${libopencore_amrwb-no}"
-echo "libopencv support         ${libopencv-no}"
-echo "libopenjpeg enabled       ${libopenjpeg-no}"
-echo "libopus enabled           ${libopus-no}"
-echo "libpulse enabled          ${libpulse-no}"
-echo "librtmp enabled           ${librtmp-no}"
-echo "libschroedinger enabled   ${libschroedinger-no}"
-echo "libspeex enabled          ${libspeex-no}"
-echo "libtheora enabled         ${libtheora-no}"
-echo "libvo-aacenc support      ${libvo_aacenc-no}"
-echo "libvo-amrwbenc support    ${libvo_amrwbenc-no}"
-echo "libvorbis enabled         ${libvorbis-no}"
-echo "libvpx enabled            ${libvpx-no}"
-echo "libx264 enabled           ${libx264-no}"
-echo "libxavs enabled           ${libxavs-no}"
-echo "libxvid enabled           ${libxvid-no}"
-echo "openssl enabled           ${openssl-no}"
-echo "zlib enabled              ${zlib-no}"
-echo "bzlib enabled             ${bzlib-no}"
 test -n "$random_seed" &&
     echo "random seed               ${random_seed}"
 echo
 
+echo "External libraries:"
+print_enabled '' $EXTERNAL_LIBRARY_LIST | print_3_columns
+echo
+
 for type in decoder encoder hwaccel parser demuxer muxer protocol filter bsf indev outdev; do
     echo "Enabled ${type}s:"
     eval list=\$$(toupper $type)_LIST