DVB media addon: Fix debug build.

- Compiling dvb.media_addon with DEBUG on fails with error message:
    generated/objects/haiku/x86/debug_1/add-ons/media/media-add-ons/dvb/
    MediaFormat.o: In function `av_log2_c': /boot/home/Development/haiku-a4/
    generated/build_packages/ffmpeg-0.10.2-r1a4-x86-gcc2-2012-08-30/common/
    include/libavutil/common.h:80: undefined reference to `ff_log2_tab'
    collect2: ld returned 1 exit status"

- Research done to narrow down the solution space:
    - ff_log2_tab is a array that is nowhere needed in the dvb.media_addon
    - ff_log2_tab is defined as an extern array in the ffmpeg header file
      libavutil/common.h
    - ff_log2_tab is used in the inline function av_log2_c (libavutil/common.h)
      which doesn't get optimized away when compiling with debug information
    - MediaFormat.cpp needs only some Codec-IDs from the ffmpeg header file
      avcodec.h

- The following fixes were tried:
    - Trying to eliminate unused debug symbols with compilation
      flag -feliminate-unused-debug-types (see gcc documentation
      http://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/Debugging-Options.html#Debugging-Options)
      by adding the following lines to UserBuildConfig
          AppendToConfigVar C++FLAGS : HAIKU_TOP src : -feliminate-unused-debug-types : global ;
          AppendToConfigVar CCFLAGS : HAIKU_TOP src : -feliminate-unused-debug-types : global ;
      -> Failed, because flag -feliminate-unused-debug-types is not supported by GCC 2.95.3

    - Trying to eliminate unused debug symbols in the linker stage
      -> This worked, by removing the LINKFLAG "-Xlinker --no-undefined" when
         linking all objects into the dvb.media_addon we are getting our addon
         with debug symbols.

- Final solution:
    - Instead of adding/removing flags, we just add the missing implementation
      for the ff_log2_tab array in MediaFormat.cpp. This -feels- the seems to
      be the cleanest solution as it is more obvious what's goin' on compared
      to hiding the solution in the Jamfile.

Signed-off-by: Colin Günther <coling@gmx.de>