BeOS patches by "shatty" <shatty at myrealbox.com>
1. errno's are negative on beos, so negating them gives positive values.
2. the -shared flag is -nostart on beos.
3. building the shared lib on beos requires -fomit-frame-pointer
4. beos doesn't have oss support

Originally committed as revision 779 to svn://svn.ffmpeg.org/ffmpeg/trunk
