Use a group() instead of a static_library()

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 851759ca2d42cb50d445d3d843080ccb2c238ad3..a636c8c2d249e97242207d3222b2f5078c478257 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -2,11 +2,16 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-static_library("libvpx") {
-  deps = [
-    "//third_party/libvpx_new",
-  ]
+# This config is applied to targets that depend on libvpx.
+config("libvpx_external_config") {
   include_dirs = [
     "//third_party/libvpx_new/source/libvpx",
   ]
 }
+
+group("libvpx") {
+  public_deps = [
+    "//third_party/libvpx_new",
+  ]
+  public_configs = [ ":libvpx_external_config" ]
+}