Add an actual 3dnow intrinsinc so the configure script doesn't just check for...

Add an actual 3dnow intrinsinc so the configure script doesn't just check for the existence of the 3dnow header

Originally committed as revision 5383 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -1110,6 +1110,7 @@ fi
 cat > $TMPC << EOF
 #include <mm3dnow.h>
 int main(void) {
+_m_femms();
 return 0;
 }
 EOF