configure: require pkg-config for libvorbis

libvorbis comes with pkg-config files since at least v1.0.1, way back in 2003.

We need the two checks for vorbis and vorbisenc because we use functions from
both and Xiph considers them separate libraries.

The check is inverted (vorbis first then vorbisenc) because add_extralibs()
prepends to EXTRALIBS instead of appending. For both shared and static linking
the order didn't seem to matter anyway, testing with MinGW.
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>

configure

@@ -5902,7 +5902,8 @@ enabled libtwolame        && require libtwolame twolame.h twolame_init -ltwolame
 enabled libv4l2           && require_pkg_config libv4l2 libv4l2.h v4l2_ioctl
 enabled libvidstab        && require_pkg_config "vidstab >= 0.98" vid.stab/libvidstab.h vsMotionDetectInit
 enabled libvo_amrwbenc    && require libvo_amrwbenc vo-amrwbenc/enc_if.h E_IF_init -lvo-amrwbenc
-enabled libvorbis         && require libvorbis vorbis/vorbisenc.h vorbis_info_init -lvorbisenc -lvorbis -logg
+enabled libvorbis         && require_pkg_config vorbis vorbis/codec.h vorbis_info_init &&
+                             require_pkg_config vorbisenc vorbis/vorbisenc.h vorbis_encode_init
 
 enabled libvpx            && {
     enabled libvpx_vp8_decoder && {