GN: Turn libvpx into a source_set to fix Mac linking issues

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.
 
 import("//build/config/arm.gni")
 import("//build/config/android/config.gni")
 import("//third_party/libvpx/libvpx_srcs.gni")
 import("//third_party/yasm/yasm_assemble.gni")
 
 if (is_posix && !is_mac) {
@@ skipping 169 matching lines @@
     if (cpu_arch_full == "arm-neon" ||
         cpu_arch_full == "arm-neon-cpu-detect") {
       cflags = [ "-mfpu=neon" ]
     }
     deps = [
       ":convert_arm_assembly",
     ]
   }
 }
 
-static_library("libvpx") {
+source_set("libvpx") {
   if (!is_debug && is_win && is_official_build) {
     configs -= [ "//build/config/compiler:optimize" ]
     configs += [ "//build/config/compiler:optimize_max" ]
   }
 
   if (current_cpu == "x86") {
     sources = libvpx_srcs_x86
   } else if (current_cpu == "x64") {
     if (is_msan) {
       sources = libvpx_srcs_generic
@@ skipping 43 matching lines @@
   }
   if (is_android) {
     deps += [ "//third_party/android_tools:cpu_features" ]
   }
   if (current_cpu == "arm") {
     deps += [ ":libvpx_assembly_arm" ]
   }
 
   public_configs = [ ":libvpx_external_config" ]
 }