[PATCH] Fix web/60933

[Richard Biener]

The GMP people complained that we "advertise" outdated versions
in our install instructions.  I tried to address that by not
explicitely listing a "good" version but only mention the version
that is the minimum requirement.  I also added a reference to
contrib/download_prerequesites as the recommended way to do
in-tree builds (so we don't get random bugreports for that
with untested combinations of gmp/mpfr/mpc versions).

We probably should try to bump the versions used by that script
to something more recent though (should we do that for the 4.9
branch even?).  Any idea what to choose here?  I'd say mpc
1.0.2 is fine, so is mpfr 3.1.2, but should we avoid the 6.0.0 version
of gmp?  We shouldn't change those versions too often, otherwise
we end up with a lot of garbage in gcc/infrastructure (we don't
want to break old versions of the script).

Meanwhile is does the patch look ok?

Thanks,
Richard.

2014-04-24  Richard Biener  <rguenther@suse.de>

	PR web/60933
	* doc/install.texi: Mention download_prerequesites as the
	recommended way to setup in-tree builds of gmp, mpfr, mpc,
	cloog and isl.  Do not advertise outdated versions of gmp,
	mpfr and mpc.

Index: gcc/doc/install.texi
===================================================================
--- gcc/doc/install.texi	(revision 209677)
+++ gcc/doc/install.texi	(working copy)
@@ -351,32 +351,41 @@ versions may work in some cases, but it'
 versions documented.  We appreciate bug reports about problems with
 newer versions, though.  If your OS vendor provides packages for the
 support libraries then using those packages may be the simplest way to
-install the libraries.
+install the libraries.  If you choose to build the library dependencies
+together with GCC you are encouraged to use the
+@command{download_prerequesites} script that comes with the GCC
+source tarball in the @file{contrib} directory.
+This downloads versions that were tested to build and
+work ok and prepares the source tree appropriately.
 
 @table @asis
-@item GNU Multiple Precision Library (GMP) version 4.3.2 (or later)
+@item GNU Multiple Precision Library (GMP)
 
-Necessary to build GCC@.  If a GMP source distribution is found in a
+Necessary to build GCC@.  It can be downloaded from @uref{https://gmplib.org/}.
+Older versions than 4.2.3 will not work.
+If a GMP source distribution is found in a
 subdirectory of your GCC sources named @file{gmp}, it will be built
 together with GCC.  Alternatively, if GMP is already installed but it
 is not in your library search path, you will have to configure with the
 @option{--with-gmp} configure option.  See also @option{--with-gmp-lib}
 and @option{--with-gmp-include}.
 
-@item MPFR Library version 2.4.2 (or later)
+@item MPFR Library
 
 Necessary to build GCC@.  It can be downloaded from
-@uref{http://www.mpfr.org/}.  If an MPFR source distribution is found
+@uref{http://www.mpfr.org/}.  Older versions than 2.4.0 will not work.
+If an MPFR source distribution is found
 in a subdirectory of your GCC sources named @file{mpfr}, it will be
 built together with GCC.  Alternatively, if MPFR is already installed
 but it is not in your default library search path, the
 @option{--with-mpfr} configure option should be used.  See also
 @option{--with-mpfr-lib} and @option{--with-mpfr-include}.
 
-@item MPC Library version 0.8.1 (or later)
+@item MPC Library
 
 Necessary to build GCC@.  It can be downloaded from
-@uref{http://www.multiprecision.org/}.  If an MPC source distribution
+@uref{http://www.multiprecision.org/}.  Older versions than
+0.8.0 will not work.  If an MPC source distribution
 is found in a subdirectory of your GCC sources named @file{mpc}, it
 will be built together with GCC.  Alternatively, if MPC is already
 installed but it is not in your default library search path, the