libm.h needs attributes.h
Originally committed as revision 22405 to svn://svn.ffmpeg.org/ffmpeg/trunk
Move libm replacements to new header libm.h
ffmpeg.c uses lrintf(), which is missing on some systems. Previouslyit picked up the replacement via libavutil/internal.h due toHAVE_AV_CONFIG_H being erroneously defined.
Moving these replacements to a separate header enables ffmpeg.c to...