build failure, GMP not available

[Paolo Bonzini]

> I wouldn't object to that.  It's a bit more build-system complexity, but 
> if it makes it easier for people, then it's worth it.

Actually, since we are at it, I would like to have toplevel configure 
automatically symlink "foo-1.2.3" to "foo".  This way, untarring 
gmp/mpfr (and maybe also bison/texinfo/whatever) would magically work.

I have not done this until now because binutils, gdb and other things 
using the gcc/src build system would not work in this scheme. :-(

Paolo