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

build/sanitizers/BUILD.gn

Index: build/sanitizers/BUILD.gn
diff --git a/build/sanitizers/BUILD.gn b/build/sanitizers/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..4f81f3ebadd0b5071c2dce7322af16251c1739bc
--- /dev/null
+++ b/build/sanitizers/BUILD.gn
@@ -0,0 +1,24 @@
+# Copyright (c) 2015 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.
+
+if (is_linux && !is_chromeos) {
+  # TODO(GYP): Figure out which of these work and are needed on other platforms.
+  copy("copy_llvm_symbolizer") {
+    if (is_win) {
+      sources = [
+        "//third_party/llvm-build/Release+Asserts/bin/llvm-symbolizer.exe",
+      ]
+      outputs = [
+        "$root_out_dir/llvm-symbolizer.exe",
+      ]
+    } else {
+      sources = [
+        "//third_party/llvm-build/Release+Asserts/bin/llvm-symbolizer",
+      ]
+      outputs = [
+        "$root_out_dir/llvm-symbolizer",
+      ]
+    }
+  }
+}