gtk3: replace bugzilla patch with local file.

pkgs/development/libraries/gtk/3.x.nix

@@ -76,12 +76,7 @@ stdenv.mkDerivation rec {
 
   patches = [
     ./patches/3.0-immodules.cache.patch
-
-    (fetchpatch {
-      name = "Xft-setting-fallback-compute-DPI-properly.patch";
-      url = "https://bug757142.bugzilla-attachments.gnome.org/attachment.cgi?id=344123";
-      sha256 = "0g6fhqcv8spfy3mfmxpyji93k8d4p4q4fz1v9a1c1cgcwkz41d7p";
-    })
+    ./patches/3.0-Xft-setting-fallback-compute-DPI-properly.patch
   ] ++ lib.optionals stdenv.isDarwin [
     # X11 module requires <gio/gdesktopappinfo.h> which is not installed on Darwin
     # let’s drop that dependency in similar way to how other parts of the library do it

pkgs/development/libraries/gtk/patches/3.0-Xft-setting-fallback-compute-DPI-properly.patch

@@ -0,0 +1,34 @@
+From 269f2d80ea41cde17612600841fbdc32e99010f5 Mon Sep 17 00:00:00 2001
+From: Giuseppe Bilotta <giuseppe.bilotta@gmail.com>
+Date: Tue, 24 Jan 2017 12:30:08 +0100
+Subject: [PATCH] Xft setting fallback: compute DPI properly
+
+This is a partial revert of bdf0820c501437a2150d8ff0d5340246e713f73f. If
+the Xft DPI settings are not explicitly set, use the values provided by
+the X server rather than hard-coding the fallback value of 96.
+
+While an auto-configured Xorg already reports 96, this value can be
+overriden by the user, and we should respect the user choice in this
+case. There is no need to require them to set the same value in
+different places (the Xorg DPI settings and Xft.dpi).
+---
+ gdk/x11/gdkxftdefaults.c | 3 ++-
+ 1 file changed, 2 insertions(+), 1 deletion(-)
+
+diff --git a/gdk/x11/gdkxftdefaults.c b/gdk/x11/gdkxftdefaults.c
+index fa1cfde2ec..c462b78c4b 100644
+--- a/gdk/x11/gdkxftdefaults.c
++++ b/gdk/x11/gdkxftdefaults.c
+@@ -174,7 +174,8 @@ init_xft_settings (GdkScreen *screen)
+     x11_screen->xft_rgba = FC_RGBA_UNKNOWN;
+ 
+   if (!get_double_default (xdisplay, "dpi", &dpi_double))
+-    dpi_double = 96.0;
++    dpi_double = (DisplayHeight(xdisplay, x11_screen->screen_num)*25.4)/
++		    DisplayHeightMM(xdisplay, x11_screen->screen_num);
+ 
+   x11_screen->xft_dpi = (int)(0.5 + PANGO_SCALE * dpi_double);
+ }
+-- 
+2.11.0.616.gd72966cf44.dirty
+