cgal_4: use fetchpatch's `relative` argument

The `gcc-12-prereq.patch` patch now includes the entire `CGAL_Core`
subdirectory, but the patch only fixes warnings so this is fine.

pkgs/development/libraries/CGAL/4.nix

@@ -18,18 +18,14 @@ stdenv.mkDerivation rec {
     (fetchpatch {
       name = "gcc-12-prereq.patch";
       url = "https://github.com/CGAL/cgal/commit/4581f1b7a8e97d1a136830e64b77cdae3546c4bf.patch";
-      sha256 = "1gzrvbrwxylv80v0m3j2s1znlysmr69lp3ggagnh38lp6423i6pq";
-      # Upstream slightly reordered directory structure since.
-      stripLen = 1;
-      # Fill patch does not apply: touches too many parts of the source.
-      includes = [ "include/CGAL/CORE/BigFloatRep.h" ];
+      relative = "CGAL_Core"; # Upstream slightly reordered directory structure since.
+      sha256 = "sha256-4+7mzGSBwAv5RHBQPAecPPKNN/LQBgvYq5mq+fHAteo=";
     })
     (fetchpatch {
       name = "gcc-12.patch";
       url = "https://github.com/CGAL/cgal/commit/6680a6e6f994b2c5b9f068eb3014d12ee1134d53.patch";
-      sha256 = "1c0h1lh8zng60yx78qc8wx714b517mil8mac87v6xr21q0b11wk7";
-      # Upstream slightly reordered directory structure since.
-      stripLen = 1;
+      relative = "CGAL_Core"; # Upstream slightly reordered directory structure since.
+      sha256 = "sha256-8kxJDT47jXI9kQNFI/ARWl9JBNS4AfU57/D0tYlgW0M=";
     })
   ];