Un-nest configs in GN files.

third_party/libwebp/BUILD.gn

Index: third_party/libwebp/BUILD.gn
diff --git a/third_party/libwebp/BUILD.gn b/third_party/libwebp/BUILD.gn
index 3259ec3fd0e8dacb5de447b434c66f7ee99f3470..d52e1da7ccfa3bd6a3fe6f9947221ee2b8518aae 100644
--- a/third_party/libwebp/BUILD.gn
+++ b/third_party/libwebp/BUILD.gn
@@ -162,6 +162,13 @@ source_set("libwebp_enc") {
   ]
 }
 
+config("libwebp_utils_warnings") {
+  if (is_clang) {
+    # See https://code.google.com/p/webp/issues/detail?id=253.
+    cflags = [ "-Wno-incompatible-pointer-types" ]
+  }
+}
+
 source_set("libwebp_utils") {
   sources = [
     "utils/bit_reader.c",
@@ -182,12 +189,6 @@ source_set("libwebp_utils") {
 
   all_dependent_configs = [ ":libwebp_config" ]
 
-  config("libwebp_utils_warnings") {
-    if (is_clang) {
-      # See https://code.google.com/p/webp/issues/detail?id=253.
-      cflags = [ "-Wno-incompatible-pointer-types" ]
-    }
-  }
   public_configs = [ ":libwebp_utils_warnings" ]
 }