libffi.so.6 not found

[Bob Bernstein <poobah%ruptured-duck.com@localhost>]

Members of this list may know that I've been successful with 
building rust. That effort was energized by another subscriber's 
attempt to build librsvg, which build-depends on rust.

With rust put to bed and tucked in, I went back to librsvg, and 
ran "make replace." That process _seemed_ to complete, but 
finished in the error "libffi.so.6 not found".

That line of text is very familiar to me; it has been haunting 
this NetBSD install for some months now. The final lines output 
by my attempted 'make replace' of librsvg are shown directly 
below:

--snip--
===> Replacing for librsvg-2.48.3nb1
===> Updating using binary package of librsvg-2.48.3nb1
/usr/bin/env  /usr/sbin/pkg_add -K /var/db/pkg -U -D 
/usr/pkgsrc/graphics/librsvg/work/.packages/librsvg-2.48.3nb1.tgz
pkg_add: librsvg-2.48.3nb1 was built to ignore ABI dependencies
/usr/pkg/lib/gio/modules/libgvfsdbus.so: Shared object 
"libffi.so.6" not found
Failed to load module: /usr/pkg/lib/gio/modules/libgvfsdbus.so
/usr/pkg/lib/gio/modules/libgvfsdbus.so: Shared object 
"libffi.so.6" not found
Failed to load module: /usr/pkg/lib/gio/modules/libgvfsdbus.so
--snip--

I _have_ libffi.so.7 built and living peaceably on this system. 
This thing has me very confused. Please sound off if any 
thoughts intrude on your metaphysical recollection..

Thank you.

--
 A test of right and wrong must be the means, one would
 think, of ascertaining what is right or wrong, and not a
 consequence of having already ascertained it.

                               J. S. Mill