This avoids symbol redefinitions problems, for example avoids the "free"
symbol to be redefined before system headers actually using it are
included, thus breaking compilation. In particular this change allows
to build FFmpeg with salsa.

Patch by matthieu castet <$surname.mat?hieu@free fr>.


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@20665 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b