Add libxdiff library

xdiff/BUILD.gn

Index: xdiff/BUILD.gn
diff --git a/xdiff/BUILD.gn b/xdiff/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..8cc00dc2095b052dfd10c7fc5129cf117ed4afc1
--- /dev/null
+++ b/xdiff/BUILD.gn
@@ -0,0 +1,31 @@
+# Copyright 2016 The Native Client Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+config("xdiff_config") {
+  visibility = [ ":*" ]
+
+  cflags = [ "-Wno-sign-compare" ]
+}
+
+static_library("xdiff") {
+  configs += [ ":xdiff_config" ]
+
+  sources = [
+    "xdiff.h",
+    "xdiffi.c",
+    "xdiffi.h",
+    "xemit.c",
+    "xemit.h",
+    "xhistogram.c",
+    "xinclude.h",
+    "xmacros.h",
+    "xmerge.c",
+    "xpatience.c",
+    "xprepare.c",
+    "xprepare.h",
+    "xtypes.h",
+    "xutils.c",
+    "xutils.h",
+  ]
+}