This issue came up during code review for JDK-7165611.

Note: If the '64' subdir stuff is only for Solaris, then it can minimally be
removed from other non-Solaris platforms. It's possible that only FDS
support added '64' subdir stuff to non-Solaris platforms.

If the '64' subdir stuff can be removed from Solaris because 32-bit
support has been removed in JDK8/HSX-25, then the '64' subdir
stuff can be removed from all platforms.

> - hotspot/make/bsd/makefiles/dtrace.make
>
> Note related to your changes but I don't think any of the "64" directory stuff has any meaning outside of Solaris.

And now that 32-bit Solaris support is being dropped, this whole '64'
subdir stuff might become obsolete/moot.