ploticus: Use gd from Nixpkgs instead of the vendored one

The gd version shipped with ploticus only contains a single font
that does not support anything but ASCII.

In order for the package to be able to render Unicode texts,
we need freetype support:

http://ploticus.sourceforge.net/doc/fonts.html

pkgs/tools/graphics/ploticus/default.nix

@@ -4,6 +4,8 @@
 , zlib
 , libX11
 , libpng
+, gd
+, freetype
 }:
 
 stdenv.mkDerivation rec {
@@ -21,12 +23,19 @@ stdenv.mkDerivation rec {
 
     # Set the location of the PREFABS directory.
     ./set-prefabs-dir.patch
+
+    # Use gd from Nixpkgs instead of the vendored one.
+    # This is required for non-ASCII fonts to work:
+    # http://ploticus.sourceforge.net/doc/fonts.html
+    ./use-gd-package.patch
   ];
 
   buildInputs = [
     zlib
     libX11
     libpng
+    gd
+    freetype
   ];
 
   hardeningDisable = [ "format" ];

pkgs/tools/graphics/ploticus/use-gd-package.patch

@@ -0,0 +1,34 @@
+--- a/src/Makefile
++++ b/src/Makefile
+@@ -91,10 +91,10 @@
+ 
+ 
+ ########### Option 1: use bundled GD16 (PNG only).  Requires libpng and zlib.
+-exetarget: plpng 
+-GD16LIBS = -lpng -lz
+-GD16H =  -I/usr/local/include
+-ZFLAG = -DWZ
++# exetarget: plpng 
++# GD16LIBS = -lpng -lz
++# GD16H =  -I/usr/local/include
++# ZFLAG = -DWZ
+ ### These should remain commented unless your libs are not in usual places, then alter to suit...
+ ### GD16LIBS = /home/scg/lib/libpng.a /home/scg/lib/libz.a
+ ### GD16H = -I/home/scg/lib
+@@ -111,11 +111,11 @@
+ 
+ ########### Option 4: use your own GD resource with FreeType2 (ttf) fonts enabled.  
+ ###########           Requires GD 1.84+, libpng, zlib, libjpeg and libfreetype
+-# exetarget: plgd18 
+-# GD18LIBS = -lgd -lpng -lz -ljpeg -lfreetype
+-# GD18H = 
+-# GDFREETYPE = -DGDFREETYPE
+-# ZFLAG = -DWZ
++exetarget: plgd18 
++GD18LIBS = -lgd -lpng -lz -ljpeg -lfreetype
++GD18H = 
++GDFREETYPE = -DGDFREETYPE
++ZFLAG = -DWZ
+ 
+ ########### Option 5: don't use GD at all.
+ # exetarget: plnogd