Explicitly enable libraries when configuring libsndfile.

If pkg-config is installed, then libsndfile's configure will try to
use pkg-config to check whether the optional dependencies (flac, ogg,
vorbis, opus, mpg123) are present.  (It will conclude that the
packages are present because the appropriate *_CFLAGS and *_LIBS are
set.)

If pkg-config isn't installed, then --enable-external-libs and
--enable-mpeg must be set explicitly in order to use these packages.

linux_build.sh

@@ -105,7 +105,8 @@ cp lame-$LAMEVERSION/include/*.h lame-$LAMEVERSION/include/lame
 curl -LO https://github.com/libsndfile/libsndfile/releases/download/$SNDFILE_VERSION/libsndfile-$SNDFILE_VERSION.tar.xz
 tar xvf libsndfile-$SNDFILE_VERSION.tar.xz
 cd $SNDFILENAME
-./configure --disable-static --disable-sqlite --disable-alsa && make -j$JOBS
+./configure --disable-static --disable-sqlite --disable-alsa --enable-external-libs --enable-mpeg
+make -j$JOBS
 cd ..
 
 cp $SNDFILENAME/src/.libs/libsndfile.so libsndfile.so