gmp: switch default version back to 5.0.5

The 5.1.0 version breaks the build of virtually every package that uses the C++
wrappers for gmp (such as mpfr, ppl, etc).

pkgs/development/libraries/gmp/5.0.5.nix

@@ -0,0 +1,55 @@
+{ stdenv, fetchurl, m4, cxx ? true }:
+
+stdenv.mkDerivation rec {
+  name = "gmp-5.0.5";
+
+  src = fetchurl {
+    url = "mirror://gnu/gmp/${name}.tar.bz2";
+    sha256 = "1jfymbr90mpn0zw5sg001llqnvf2462y77vgjknrmfs1rjn8ln0z";
+  };
+
+  nativeBuildInputs = [ m4 ];
+
+  configureFlags =
+    # Build a "fat binary", with routines for several sub-architectures
+    # (x86), except on Solaris where some tests crash with "Memory fault".
+    # See <http://hydra.nixos.org/build/2760931>, for instance.
+    (stdenv.lib.optional (!stdenv.isSunOS) "--enable-fat")
+    ++ (if cxx then [ "--enable-cxx" ] else [ "--disable-cxx" ]);
+
+  doCheck = true;
+
+  enableParallelBuilding = true;
+
+  meta = {
+    description = "GMP, the GNU multiple precision arithmetic library";
+
+    longDescription =
+      '' GMP is a free library for arbitrary precision arithmetic, operating
+         on signed integers, rational numbers, and floating point numbers.
+         There is no practical limit to the precision except the ones implied
+         by the available memory in the machine GMP runs on.  GMP has a rich
+         set of functions, and the functions have a regular interface.
+
+         The main target applications for GMP are cryptography applications
+         and research, Internet security applications, algebra systems,
+         computational algebra research, etc.
+
+         GMP is carefully designed to be as fast as possible, both for small
+         operands and for huge operands.  The speed is achieved by using
+         fullwords as the basic arithmetic type, by using fast algorithms,
+         with highly optimised assembly code for the most common inner loops
+         for a lot of CPUs, and by a general emphasis on speed.
+
+         GMP is faster than any other bignum library.  The advantage for GMP
+         increases with the operand sizes for many operations, since GMP uses
+         asymptotically faster algorithms.
+      '';
+
+    homepage = http://gmplib.org/;
+    license = "LGPLv3+";
+
+    maintainers = [ stdenv.lib.maintainers.ludo stdenv.lib.maintainers.simons ];
+    platforms = stdenv.lib.platforms.all;
+  };
+}

pkgs/top-level/all-packages.nix

@@ -3768,7 +3768,9 @@ let
   # The GHC bootstrap binaries link against libgmp.so.3, which is in GMP 4.x.
   gmp4 = callPackage ../development/libraries/gmp/4.3.2.nix { };
 
-  gmp5 = callPackage ../development/libraries/gmp/5.1.0.nix { };
+  gmp5 = callPackage ../development/libraries/gmp/5.0.5.nix { };
+
+  gmp51 = callPackage ../development/libraries/gmp/5.1.0.nix { };
 
   gobjectIntrospection = callPackage ../development/libraries/gobject-introspection { };