win clang: don't disable -Wself-assign

third_party/libpng/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("libpng_config") {
   include_dirs = [ "." ]
 
   defines = [
     "CHROME_PNG_WRITE_SUPPORT",
     "PNG_USER_CONFIG",
@@ skipping 43 matching lines @@
 
   if (is_win && is_component_build) {
     defines = [ "PNG_BUILD_DLL" ]
   }
 
   public_configs = [ ":libpng_config" ]
 
   public_deps = [
     "//third_party/zlib",
   ]
+
+  # 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" ]
 }
 
 if (is_win) {
   component("libpng") {
     public_deps = [
       ":libpng_sources",
     ]
   }
 } else {
   group("libpng") {
     public_deps = [
       ":libpng_sources",
     ]
   }
 }