Once you have libswf all you need to do is to configure --with-swf[=DIR] where DIR is a location
containing the directories include and lib. The include directory
has to contain the swf.h file and the lib directory
has to contain the libswf.a file. If you unpack the
libswf distribution the two files will be in one directory. Consequently
you will have to copy the files to the proper location manually.