librtmp may link to different ssl implementations

Make sure we link using the right libs by using pkg-config

Originally committed as revision 23511 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -2617,7 +2617,7 @@ enabled libnut     && require  libnut libnut.h nut_demuxer_init -lnut
 enabled libopencore_amrnb  && require libopencore_amrnb opencore-amrnb/interf_dec.h Decoder_Interface_init -lopencore-amrnb -lm
 enabled libopencore_amrwb  && require libopencore_amrwb opencore-amrwb/dec_if.h D_IF_init -lopencore-amrwb -lm
 enabled libopenjpeg && require libopenjpeg openjpeg.h opj_version -lopenjpeg
-enabled librtmp    && require  librtmp librtmp/rtmp.h RTMP_Init -lrtmp
+enabled librtmp    && require  librtmp librtmp/rtmp.h RTMP_Init $(pkg-config --libs librtmp)
 enabled libschroedinger && add_cflags $(pkg-config --cflags schroedinger-1.0) &&
                            require libschroedinger schroedinger/schro.h schro_init $(pkg-config --libs schroedinger-1.0)
 enabled libspeex   && require  libspeex speex/speex.h speex_decoder_init -lspeex