sage: fix build

closes #17842

pkgs/applications/science/math/sage/default.nix

@@ -7,7 +7,7 @@ stdenv.mkDerivation rec {
   name = "sage-6.8";
 
   src = fetchurl {
-    url = "mirror://sagemath/${name}.tar.gz";
+    url = "http://old.files.sagemath.org/src-old/${name}.tar.gz";
     sha256 = "102mrzzi215g1xn5zgcv501x9sghwg758jagx2jixvg1rj2jijj9";
   };
 
@@ -18,11 +18,14 @@ stdenv.mkDerivation rec {
 
   enableParallelBuilding = true;
 
+  hardeningDisable = [ "format" ];
+
   preConfigure = ''
     export SAGE_NUM_THREADS=$NIX_BUILD_CORES
     export SAGE_ATLAS_ARCH=fast
     mkdir -p $out/sageHome
     export HOME=$out/sageHome
+    export CPPFLAGS="-P"
   '';
 
   preBuild = "patchShebangs build";
@@ -30,7 +33,6 @@ stdenv.mkDerivation rec {
   installPhase = ''DESTDIR=$out make install'';
 
   meta = {
-    broken = true;
     homepage = "http://www.sagemath.org";
     description = "A free open source mathematics software system";
     license = stdenv.lib.licenses.gpl2Plus;