Make sure native W32 print dialog uses visual styles

For that to happen the libgtk3 is embedded with a manifest that requests
common controls library 6.x, and GTK lazily calls InitCommonControlsEx()
to initialize those. Then this manifest is used to temporarily override
the process activation contest when loading comdlg32 (which contains the
code for the print dialog), ensuring that it too depends on common
controls 6.x, even if the application that uses GTK does not.

https://bugzilla.gnome.org/show_bug.cgi?id=733773

gtk/libgtk3.manifest.in

@@ -0,0 +1,21 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0">
+  <assemblyIdentity
+      version="1.0.0.0"
+      processorArchitecture="@EXE_MANIFEST_ARCHITECTURE@"
+      name="libgtk3"
+      type="win32"
+  />
+  <dependency>
+    <dependentAssembly>
+      <assemblyIdentity
+          type="win32"
+          name="Microsoft.Windows.Common-Controls"
+          version="6.0.0.0"
+          processorArchitecture="@EXE_MANIFEST_ARCHITECTURE@"
+          publicKeyToken="6595b64144ccf1df"
+          language="*"
+      />
+    </dependentAssembly>
+  </dependency>
+</assembly>