Fix Windows FFmpeg configure link flags

tools/chatgui/ffmpeg/build_ffmpeg.sh

@@ -240,7 +240,6 @@ CONFIGURE_ARGS=(
     --pkg-config-flags=--static
     --extra-cflags="-I$INSTALL_DIR/include"
     --extra-ldflags="-L$INSTALL_DIR/lib"
-    --extra-libs="-lpthread -lm -ldl"
     --enable-libx264 --enable-libx265 --enable-libvpx --enable-libaom --enable-libvpl --enable-nvenc
     --enable-demuxer=avi --enable-demuxer=matroska --enable-demuxer=mov
     --enable-protocol=file --enable-parsers
@@ -250,6 +249,12 @@ CONFIGURE_ARGS=(
     --disable-ffprobe --disable-ffplay --disable-ffmpeg --disable-debug --enable-optimizations
 )
 
+if [ "$PLATFORM" = "windows" ]; then
+    CONFIGURE_ARGS+=(--extra-libs="-lpthread -lm")
+else
+    CONFIGURE_ARGS+=(--extra-libs="-lpthread -lm -ldl")
+fi
+
 DECODERS=(h264 hevc av1 vp8 vp9 mpeg4 mpeg2video mpeg1video mjpeg h263 msmpeg4v3 wmv1 wmv2 vc1
     aac mp3 opus vorbis flac ac3 eac3 alac wmav1 wmav2 pcm_s16le pcm_s24le pcm_s32le pcm_u8 pcm_f32le)
 ENCODERS=(libx264 libx265 libvpx_vp9 libaom_av1 h264_nvenc hevc_nvenc av1_nvenc