openjdk8: fix build with GCC 14 (#359522)

pkgs/development/compilers/openjdk/generic.nix

···
               "-std=gnu++98"
               "-Wno-error"
             ]
+            ++ [
+              # error by default in GCC 14
+              "-Wno-error=int-conversion"
+              "-Wno-error=incompatible-pointer-types"
+            ]
           );
 
       NIX_LDFLAGS = lib.concatStringsSep " " (