add AM_PROG_AS, although currently it is only needed for PowerPC
add AM_PROG_AS, although currently it is only needed for PowerPC

LordJZ/libflac,kode54/flac,waitman/flac,fredericgermain/flac,kode54/flac,waitman/flac,LordJZ/libflac,waitman/flac,kode54/flac,Distrotech/flac,Distrotech/flac,LordJZ/libflac,fredericgermain/flac,waitman/flac,fredericgermain/flac,Distrotech/flac,kode54/flac,Distrotech/flac,LordJZ/libflac,waitman/flac,fredericgermain/flac