Add the necessary 'strip' commands to the BSD/OS section of configure because

Add the necessary 'strip' commands to the BSD/OS section of configure because
BSD/OS does not like shared libraries without a symbol table and gives errors
when linking against libavcodec.so otherwise.
patch by Steven M. Schultz < sms == at == 2BSD == dot == COM >

Originally committed as revision 4722 to svn://svn.ffmpeg.org/ffmpeg/trunk