[Patch] Bump minimum required MPFR version

[Janne Blomqvist <blomqvist dot janne at gmail dot com>]

Hi,

in http://gcc.gnu.org/install/prerequisites.html we say that GCC
requires at least MPFR 2.4.2, but in the toplevel configure.ac we only
require 2.3.1, printing a warning that the result is likely to be
buggy if the version is lower than 2.4.2.

The attached patch bumps the minimum version to 2.4.0. We started
requiring 2.3.1, which was released on 2008-01-29, on 2009-04-08, that
is, about 1 year and a few months after the release. MPFR 2.4.0 was
released on 2009-01-26, so by now it's 3 years old. And by the time we
release 4.8 it's most likely over 4 years old already.

For some background, the fortran frontend recently started using
mpfr_fmod to fix some bugs in the constant folding of the MOD and
MODULO intrinsics, effectively requiring at least MPFR 2.4.0 in order
to build.

Also, if this patch is accepted the middle-end could be modified to
constant fold BUILT_IN_FMOD{F,,L} relatively easily, something which
isn't done today.

Ok for trunk?


2012-05-06  Janne Blomqvist  <jb@gcc.gnu.org>

	* configure.ac: Bump minimum MPFR version to 2.4.0.
	* configure: Regenerated.


-- 
Janne Blomqvist

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