Factor configure-time gcc version checks (patch 1/4 for PR 7305)

[Richard Sandiford]

DJ Delorie <dj@redhat.com> writes:
> Sorry for missing this.  This is OK with me.  Please make sure both
> src and gcc are updated, for those files that are common (TL and
> config).

Thanks, installed to src/ and gcc/.  If you have time, could you
look at the two follow-up patches as well?

    http://gcc.gnu.org/ml/gcc-patches/2004-11/msg02186.html
    http://gcc.gnu.org/ml/gcc-patches/2004-11/msg02188.html

TIA.

> At some future time, it might be useful to handle the case where an
> in-tree gcc is not available, and it may use $(CC) somehow.

FWIW, the version check in gcc-version.m4 does have a stab,
but I don't know how effective it is:

> + if test -f "${gcc_version_trigger}"; then
> +   gcc_version_full=`grep version_string "${gcc_version_trigger}" | sed -e 's/.*"\([^"]*\)".*/\1/'`
> + else
> +   gcc_version_full=`$CC -v 2>&1 | sed -n 's/^gcc version //p'`
> + fi

(That bit was copied verbatim from config.if, which the first patch
above deletes.)

Richard