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

build/config/clang/BUILD.gn

Index: build/config/clang/BUILD.gn
diff --git a/build/config/clang/BUILD.gn b/build/config/clang/BUILD.gn
new file mode 100644
index 0000000000000000000000000000000000000000..6dff4863a5e93603a89a1fce1972bb8f1e70d828
--- /dev/null
+++ b/build/config/clang/BUILD.gn
@@ -0,0 +1,62 @@
+# Copyright (c) 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.
+
+import("clang.gni")
+
+config("find_bad_constructs") {
+  if (clang_use_chrome_plugins) {
+    cflags = []
+
+    # On Windows, the plugin is built directly into clang, so there's
+    # no need to load it dynamically.
+
+    if (is_mac || is_ios) {
+      cflags += [
+        "-Xclang",
+        "-load",
+        "-Xclang",
+        rebase_path(
+            "//third_party/llvm-build/Release+Asserts/lib/libFindBadConstructs.dylib",
+            root_build_dir),
+      ]
+    } else if (is_linux) {
+      cflags += [
+        "-Xclang",
+        "-load",
+        "-Xclang",
+        rebase_path(
+            "//third_party/llvm-build/Release+Asserts/lib/libFindBadConstructs.so",
+            root_build_dir),
+      ]
+    }
+
+    # https://crbug.com/441916
+    if (is_android || is_linux || is_mac) {
+      cflags += [
+        "-Xclang",
+        "-plugin-arg-find-bad-constructs",
+        "-Xclang",
+        "check-templates",
+      ]
+    }
+
+    cflags += [
+      "-Xclang",
+      "-add-plugin",
+      "-Xclang",
+      "find-bad-constructs",
+    ]
+  }
+}
+
+# Enables some extra Clang-specific warnings. Some third-party code won't
+# compile with these so may want to remove this config.
+config("extra_warnings") {
+  cflags = [
+    "-Wheader-hygiene",
+
+    # Warns when a const char[] is converted to bool.
+    "-Wstring-conversion",
+  ]
+}