Fix detection of swscale with compile/link test.

configure.ac

@@ -3097,13 +3097,13 @@ dnl Trying with pkg-config
      VLC_ADD_LIBS([ffmpeg stream_out_switcher],[${FFMPEG_LIBS}])
 
      dnl even newer ffmpeg has a libswscale
-     PKG_CHECK_MODULES(SWSCALE,[libavutil, libswscale],[
+     PKG_CHECK_MODULES(SWSCALE,[libswscale],[
        VLC_ADD_CFLAGS([ffmpeg],[${SWSCALE_CFLAGS}])
        VLC_ADD_LIBS([ffmpeg],[${SWSCALE_LIBS}])
-       AC_CHECK_HEADERS(ffmpeg/swscale.h, [], [AC_MSG_ERROR([Missing header file ffmpeg/swscale.h.])])
-dnl       AC_CHECK_LIB(swscale, sws_getContext,
-dnl         [AC_CHECK_HEADERS([ffmpeg/avutil.h, ffmpeg/swscale.h])],[])
-dnl       ],[ true ])
+dnl    AC_CHECK_HEADERS(ffmpeg/swscale.h, [], [AC_MSG_ERROR([Missing header file ffmpeg/swscale.h.])])
+       AC_CHECK_LIB(swscale, sws_getContext,
+         [AC_CHECK_HEADERS([ffmpeg/avutil.h, ffmpeg/swscale.h])],[],[-lavutil -lm])
+       ],[ true ])
      VLC_RESTORE_FLAGS
     ],[