win clang: don't disable -Wself-assign

third_party/lzma_sdk/BUILD.gn

 # Copyright 2014 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.
 
 config("lzma_sdk_config") {
   include_dirs = [ "." ]
 }
 
 static_library("lzma_sdk") {
   sources = [
@@ skipping 35 matching lines @@
 
   defines = [
     "_7ZIP_ST",
     "_LZMA_PROB32",
   ]
 
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [ "//build/config/compiler:no_chromium_code" ]
 
   public_configs = [ ":lzma_sdk_config" ]
+
+  # Must be in a config because of how GN orders flags (otherwise -Wall will
+  # appear after this, and turn it back on).
+  config("clang_warnings") {
+    if (is_clang) {
+      # Upstream uses self-assignment to avoid warnings.
+      cflags = [ "-Wno-self-assign" ]
+    }
+  }
+  configs += [ ":clang_warnings" ]
 }