support for building dynamic libraries on Mac OS X

based on a patch by Lina Pezzella <J4rg0n -- at -- gentoo -- dot -- org>

Originally committed as revision 4616 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -329,11 +329,12 @@ v4l="no"
 audio_oss="no"
 dv1394="no"
 ffserver="no"
-SHFLAGS="-dynamiclib"
+SHFLAGS="-dynamiclib -Wl,-single_module,-undefined,dynamic_lookup"
 extralibs=""
 darwin="yes"
 strip="strip -x"
-LDFLAGS="-Wl,-search_paths_first"
+LDFLAGS="-Wl,-dynamic,-search_paths_first"
+SLIBSUF=".dylib"
 FFSLDFLAGS=-Wl,-bind_at_load
 ;;
 MINGW32*)
@@ -1428,6 +1429,8 @@ fi
 if test "$lshared" = "yes" ; then
   echo "BUILD_SHARED=yes" >> config.mak
   echo "PIC=-fPIC -DPIC" >> config.mak
+  echo "SPPMAJOR=0" >> config.mak
+  echo "SPPVERSION=0.0.1" >> config.mak 
 fi
 echo "EXTRALIBS=$extralibs" >> config.mak
 version=`grep '#define FFMPEG_VERSION ' "$source_path/libavcodec/avcodec.h" |