Revert of Un-nest configs in GN files.

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",
   ]
 
   if (is_android) {
     #'toolsets': ['target', 'host'],
     defines += [ "CHROME_PNG_READ_PACK_SUPPORT" ]  # Required by freetype.
   }
 
   if (is_win) {
     if (is_component_build) {
       defines += [
         "PNG_USE_DLL",
         "PNG_NO_MODULEDEF",
       ]
     }
   }
 }
 
-# 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" ]
-  }
-}
-
 source_set("libpng_sources") {
   sources = [
     "png.c",
     "png.h",
     "pngconf.h",
     "pngerror.c",
     "pnggccrd.c",
     "pngget.c",
     "pngmem.c",
     "pngpread.c",
@@ skipping 17 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",
     ]
   }
 }