pcb2gcode: cherry-pick patch from upstream to fix build

The build failure shown here:

  https://hydra.nixos.org/build/176023034

Is fixed upstream, but they have not made a new release yet.  Let's
cherry-pick their fix until the next release.

pkgs/tools/misc/pcb2gcode/default.nix

@@ -9,6 +9,7 @@
 , gerbv
 , librsvg
 , bash
+, fetchpatch
 }:
 
 stdenv.mkDerivation rec {
@@ -22,6 +23,15 @@ stdenv.mkDerivation rec {
     sha256 = "sha256-3VQlYtSi6yWWNuxTlBzvBtkM5hAss47xat+sEW+P79E=";
   };
 
+  patches = [
+    # the patch below is part of upstream mainline, we can remove this
+    # when they make their next release
+    (fetchpatch {
+      url = "https://github.com/pcb2gcode/pcb2gcode/commit/01cd18a6d859ab1aac6c532c99be9109f083448d.patch";
+      sha256 = "sha256-5hl8KsDxSWMzXS3oRG0fBfHFq0IpZ//sU8lfY9Yp8L0=";
+    })
+  ];
+
   nativeBuildInputs = [ autoreconfHook pkg-config ];
 
   buildInputs = [ boost glibmm gtkmm2 gerbv librsvg ];