Add a snapshot of flutter/engine/src/build to our sdk

build/linux/unbundle/libxslt.gyp

Index: build/linux/unbundle/libxslt.gyp
diff --git a/build/linux/unbundle/libxslt.gyp b/build/linux/unbundle/libxslt.gyp
new file mode 100644
index 0000000000000000000000000000000000000000..f7f6bb9ab02584f13d1d76dd26b94737c5267f1a
--- /dev/null
+++ b/build/linux/unbundle/libxslt.gyp
@@ -0,0 +1,25 @@
+# Copyright 2013 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+{
+  'targets': [
+    {
+      'target_name': 'libxslt',
+      'type': 'none',
+      'direct_dependent_settings': {
+        'cflags': [
+          '<!@(pkg-config --cflags libxslt)',
+        ],
+      },
+      'link_settings': {
+        'ldflags': [
+          '<!@(pkg-config --libs-only-L --libs-only-other libxslt)',
+        ],
+        'libraries': [
+          '<!@(pkg-config --libs-only-l libxslt)',
+        ],
+      },
+    },
+  ],
+}