the check on platforms that require those flags.
patch by Michael Kostylev, mik niipt ru
Originally committed as revision 11553 to svn://svn.ffmpeg.org/ffmpeg/trunk
and provide simple replacements if they are unavailable.
patch by Michael Kostylev, mik niipt ru
Originally committed as revision 11326 to svn://svn.ffmpeg.org/ffmpeg/trunk