libffi does not respect libdir configuration

[Paolo Borelli]

Hi,

    as far as I can see it seems libffi always installs in the
$(prefix)/lib64 directory, even when building with a specifc
--libdir=$prefix/lib configuration.

I am seeing this problem on a centos 6 system when building the 3.0.13 tarball.

This is a major problem when trying to build the gtk stack since
jhbuild (which is gtk's conventional build tool) enforces the use of
lib over lib64 for all the other libraries.


Thanks,

     Paolo