Problematic linking between glibc and shared libgcc

[Richard Kenner]

    That's really odd. In the GNAT world, we have only recently started to
    build shared runtime libraries, in some cases now as the default, and
    we are doing it because of demand by some of our users working on
    large projects.

Not really odd.  libgcc is *tiny* and the GNAT runtime library is quite
large.  Also, there are issues relating to conflicts (in the EH code)
between libgcc and glibc.  Unlike the GNAT RTS, very few C programs use
any code from libgcc, so the advantage of having it shared is much less
and the potential for problems of conflicts with glibc is the downside.