Log Message:
FLAC recently gained PPC optimizations that only work with Apple's
assembler.  Since they cause the FLAC build to fail on AIX and NetBSD,
only enable the optimizations if the OPSYS is Darwin.

There is also a misplaced #endif in lpc.h that causes the build to
fail on all platforms if assembler optimizations are disabled.  This
is fixed by patch-af.

Thanks to Michael <macallan18@earthlink.net> for troubleshooting!