netpbm: Hardcode rgb.txt path

We did that in the past with rgbpaths.patch in the past but it was eventually removed. This fixes the regression.

pkgs/tools/graphics/netpbm/default.nix

@@ -65,6 +65,9 @@ stdenv.mkDerivation {
     echo "TIFFLIB_NEEDS_JPEG = N" >> config.mk
     echo "TIFFLIB_NEEDS_Z = N" >> config.mk
     echo "JPEGLIB = libjpeg.so" >> config.mk
+
+    # Fix path to rgb.txt
+    echo "RGB_DB_PATH = $out/share/netpbm/misc/rgb.txt" >> config.mk
   '' + stdenv.lib.optionalString stdenv.isDarwin ''
     echo "LDSHLIB=-dynamiclib -install_name $out/lib/libnetpbm.\$(MAJ).dylib" >> config.mk
     echo "NETPBMLIBTYPE = dylib" >> config.mk