Separate out target defaults in the GN build config.

build/split_static_library.gni

 # Copyright 2016 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.
 
 template("split_static_library") {
   assert(defined(invoker.split_count),
          "Must define split_count for split_static_library")
 
   # In many conditions the number of inputs will be 1 (because the count will
   # be conditional on platform or configuration) so optimize that.
@@ skipping 33 matching lines @@
     group(group_name) {
       public_deps = generated_static_libraries
       forward_variables_from(invoker,
                              [
                                "testonly",
                                "visibility",
                              ])
     }
   }
 }
+
+set_defaults("split_static_library") {
+  configs = default_compiler_configs
+}