cgal_4: pull upstream fir for c++17

Without the change the build fails on gcc-12 as:

    /build/source/include/CGAL/CORE/BigFloatRep.h:437:10:
      error: use of deleted function 'std::...::basic_string(std::nullptr_t)
        [with _CharT = char; ...; std::nullptr_t = std::nullptr_t]'
      437 |   return NULL;
          |          ^~~~

pkgs/development/libraries/CGAL/4.nix

@@ -1,4 +1,4 @@
-{ lib, stdenv, fetchFromGitHub, cmake, boost, gmp, mpfr }:
+{ lib, stdenv, fetchFromGitHub, fetchpatch, cmake, boost, gmp, mpfr }:
 
 stdenv.mkDerivation rec {
   version = "4.14.2";
@@ -11,6 +11,28 @@ stdenv.mkDerivation rec {
     sha256 = "1p1xyws2s9h2c8hlkz1af4ix48qma160av24by6lcm8al1g44pca";
   };
 
+  patches = [
+
+    # Pull upstream fix for c++17 (gcc-12):
+    #  https://github.com/CGAL/cgal/pull/6109
+    (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" ];
+    })
+    (fetchpatch {
+      name = "gcc-12.patch";
+      url = "https://github.com/CGAL/cgal/commit/6680a6e6f994b2c5b9f068eb3014d12ee1134d53.patch";
+      sha256 = "1c0h1lh8zng60yx78qc8wx714b517mil8mac87v6xr21q0b11wk7";
+      # Upstream slightly reordered directory structure since.
+      stripLen = 1;
+    })
+  ];
+
   # note: optional component libCGAL_ImageIO would need zlib and opengl;
   #   there are also libCGAL_Qt{3,4} omitted ATM
   buildInputs = [ boost gmp mpfr ];