Build using --with-gmp and shared libraries

[Paolo Bonzini]

> This patch has both a toplevel part and a part in gcc/, so I don't
> know exactly who can approve it.

I haven't really understood why you need this patch.

If you need to set the LD_LIBRARY_PATH manually after installation, 
something is broken.  If the GMPLIBSDIR is for example something in your 
home directory, the solution is not to patch gcc and maybe other 
mpfr-using programs that you are a developer of: rather, the solution is 
to add $HOME/lib to the search path in your .profile file.

If you need this patch because you're running `make check' with a 
non-installed copy of gmp/mpfr, I'm not sure this is something that we 
want to support.  It would be a different story, of course, if mpfr 
could be dropped into a unified tree and the in-tree mpfr would be used 
by GCC: but in this case the in-tree mpfr would be added to the 
LD_LIBRARY_PATH automatically, just like libbfd is.

As a side note, making an in-tree mpfr possible is something easy to do, 
that I'd endorse, and that I could help with (unlike moving libgcc to 
the toplevel ;-).

Or did I miss the point entirely?

Paolo