libffi not installed

[Nathanael Nerode]

>Today I did a clean build and install of the trunk, and I noticed that
>libffi is not installed.
>
>I see this in the top-level Makefile.in:
>
># Dummy target for uninstallable.
>install-target-libffi:
>
>I'd prefer it if libffi install decisions were left up to the libffi
>Makefile.
>
>Tom

This reproduced existing behavior prior to my cleanups; I found that 
several subdirectories were never installed and reproduced that.

If libffi provides a functioning "install" target (even if it's a dummy target 
which does nothing) this can be removed safely.

Note the following line in Makefile.def:

target_modules = { module= libffi; no_install=true; };

Just remove the "no_install=true;" and regenerate Makefile.in if you 
want libffi to be installable.  Happy?

--Nathanael