singular: use gcc5

Progress on: #28643
Fixes: #29682

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

@@ -15,8 +15,8 @@ stdenv.mkDerivation rec {
   nativeBuildInputs = [ autoconf bison pkgconfig ];
 
   preConfigure = ''
-    find . -exec sed -e 's@/bin/rm@${coreutils}&@g' -i '{}' ';'
-    find . -exec sed -e 's@/bin/uname@${coreutils}&@g' -i '{}' ';'
+    find . -type f -exec sed -e 's@/bin/rm@${coreutils}&@g' -i '{}' ';'
+    find . -type f -exec sed -e 's@/bin/uname@${coreutils}&@g' -i '{}' ';'
     ${stdenv.lib.optionalString asLibsingular ''NIX_CFLAGS_COMPILE="$NIX_CFLAGS_COMPILE -DLIBSINGULAR"''}
   '';
 

pkgs/top-level/all-packages.nix

@@ -18565,9 +18565,12 @@ with pkgs;
     inherit (gnome3) gtksourceview;
   };
 
-  singular = callPackage ../applications/science/math/singular {};
+  singular = callPackage ../applications/science/math/singular {
+    stdenv = overrideCC stdenv gcc5;
+  };
   libsingular = callPackage ../applications/science/math/singular {
     asLibsingular = true;
+    stdenv = overrideCC stdenv gcc5;
   };
 
   scilab = callPackage ../applications/science/math/scilab {