Dear Prof. Bagnara,
We discovered, though, that things stop working for us in passing from the versions distributed with with Gettext 0.14.6 to the versions distributed with Gettext 0.15.
The change between lib-link.m4 of version 0.14.6 and 0.15 is that before, it assumed the libraries to be installed in $prefix/lib. In 0.15, on Linux bi-arch systems, i.e. systems which have the system libraries both in 32-bit mode and in 64-bit mode, when you are compiling in 64-bit mode, the macros will look for the libraries in $prefix/lib64 rather than in $prefix/lib.
In 0.18 (or already with the macros in gnulib today) a similar change is done for Solaris bi-arch systems.
For you, the simple fix is cd $prefix ln -s lib lib64
The vendor conventions on bi-arch Linux systems are to store 32-bit libraries in $prefix/lib and 64-bit libraries in $prefix/lib64. Unfortunately this does not coincide with the GNU default $(libdir), which is $prefix/lib always. Feel free to follow-up to the discussion started at http://lists.gnu.org/archive/html/autoconf/2008-09/msg00059.html
Bruno