Un-nest configs in GN files.

third_party/libxml/BUILD.gn

 # 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.
 
 # Define an "os_include" variable that points at the OS-specific generated
 # headers.  These were generated by running the configure script offline.
 if (is_linux || is_android || is_nacl) {
   os_include = "linux"
 } else if (is_mac || is_ios) {
   os_include = "mac"
 } else if (is_win) {
   os_include = "win32"
 }
 
 config("libxml_config") {
   # Define LIBXML_STATIC as nothing to match how libxml.h (an internal header)
   # defines LIBXML_STATIC, otherwise we get the macro redefined warning from
   # GCC. ("defines" does "-DFOO" which defines the macro FOO as 1.)
   cflags = [ "-DLIBXML_STATIC=" ]
 
   include_dirs = [
     "src/include",
     "$os_include/include",
   ]
 }
 
+config("libxml_warnings") {
+  if (is_win) {
+    cflags_c = [
+      "/wd4018",  # Signed/unsigned mismatch in comparison.
+      "/wd4101",  # Unreferenced local variable.
+    ]
+  }
+  if (is_clang) {
+    cflags = [
+      # libxml passes `const unsigned char*` through `const char*`.
+      "-Wno-pointer-sign",
+
+      # pattern.c and uri.c both have an intentional `for (...);` /
+      # `while(...);` loop. I submitted a patch to move the `'` to its own
+      # line, but until that's landed suppress the warning:
+      "-Wno-empty-body",
+
+      # debugXML.c compares array 'arg' to NULL.
+      "-Wno-tautological-pointer-compare",
+
+      # threads.c attempts to forward declare a pthread_equal which doesn't
+      # match the prototype in pthreads.h
+      "-Wno-ignored-attributes",
+
+      # libxml casts from int to long to void*.
+      "-Wno-int-to-void-pointer-cast",
+
+      # libxml passes a volatile LPCRITICAL_SECTION* to a function expecting
+      # a void* volatile*.
+      "-Wno-incompatible-pointer-types",
+
+      # trio_is_special_quantity and trio_is_negative are only
+      # used with certain preprocessor defines set.
+      "-Wno-unused-function",
+    ]
+  }
+}
+
 static_library("libxml") {
   output_name = "libxml2"
   sources = [
     "chromium/libxml_utils.cc",
     "chromium/libxml_utils.h",
     "linux/config.h",
     "linux/include/libxml/xmlversion.h",
     "mac/config.h",
     "mac/include/libxml/xmlversion.h",
     "src/DOCBparser.c",
@@ skipping 100 matching lines @@
     "src/xpath.c",
     "src/xpointer.c",
 
     #"src/xzlib.c",
     "src/xzlib.h",
     "win32/config.h",
     "win32/include/libxml/xmlversion.h",
   ]
 
   configs -= [ "//build/config/compiler:chromium_code" ]
-  configs += [ "//build/config/compiler:no_chromium_code" ]
+  configs += [
+    "//build/config/compiler:no_chromium_code",
+
+    # Must be after no_chromium_code for warning flags to be ordered correctly.
+    ":libxml_warnings",
+  ]
 
   public_configs = [ ":libxml_config" ]
   public_deps = [
     "//third_party/icu:icuuc",
   ]
   deps = [
     "//third_party/zlib",
   ]
 
-  if (is_win) {
-    cflags_c = [
-      "/wd4018",  # Signed/unsigned mismatch in comparison.
-      "/wd4101",  # Unreferenced local variable.
-    ]
-  } else if (is_mac || is_ios || is_android) {
+  if (is_mac || is_ios || is_android) {
     # http://www.xmlsoft.org/threads.html says that this is required when using
     # libxml from several threads, which can possibly happen in chrome. On
     # linux, this is picked up by transitivity from pkg-config output from
     # build/linux/system.gyp.
     defines = [ "_REENTRANT" ]
   }
 
-  config("libxml_warnings") {
-    if (is_clang) {
-      cflags = [
-        # libxml passes `const unsigned char*` through `const char*`.
-        "-Wno-pointer-sign",
-
-        # pattern.c and uri.c both have an intentional `for (...);` /
-        # `while(...);` loop. I submitted a patch to move the `'` to its own
-        # line, but until that's landed suppress the warning:
-        "-Wno-empty-body",
-
-        # debugXML.c compares array 'arg' to NULL.
-        "-Wno-tautological-pointer-compare",
-
-        # threads.c attempts to forward declare a pthread_equal which doesn't
-        # match the prototype in pthreads.h
-        "-Wno-ignored-attributes",
-
-        # libxml casts from int to long to void*.
-        "-Wno-int-to-void-pointer-cast",
-
-        # libxml passes a volatile LPCRITICAL_SECTION* to a function expecting
-        # a void* volatile*.
-        "-Wno-incompatible-pointer-types",
-
-        # trio_is_special_quantity and trio_is_negative are only
-        # used with certain preprocessor defines set.
-        "-Wno-unused-function",
-      ]
-    }
-  }
-  configs += [ ":libxml_warnings" ]
-
   include_dirs = [ "$os_include" ]
 }