Require GCC 4.4 or later to build glibc

[Roland McGrath]

> > Agreed.  Each individual release can say somewhere that goes into the
> > tarball what the latest version it has been built and tested with at the
> > time of release is.
> 
> we have that info somewhat in the wiki with the testing results matrix.  i 
> don't like having static released tarballs refer to a wiki entry that can go 
> away in X years, but maybe i'm just pessimistic.

People who get the tarball (and possibly keep it for N years) should not
need to go out to the web to find essential information about the release
in that tarball.  That's why we have the INSTALL file in the tarball.