audio/maplay: Fix DragonFly breakage

This package has been broken at least since DragonFly moved to gcc44 for
their base compiler.  The previously deprecated "-m486" is no longer
recognized, but the -march defaults to i486 now anyway, so this switch is
no longer required.

GCC 4.4 got rid of the iostream and iomanip backwards compatibility, so
trying to include these headers is another source of breakage.  While
probably correct for all platforms, this commit conservatively only
changes the build process for DragonFly since maplay apparently is
building okay on NetBSD.

No PKGREVISION bump is required.

(marino)