Convert libyuv to a static library in GN.

BUILD.gn

 # Copyright 2014 The LibYuv Project Authors. All rights reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS. All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 import("//build/config/arm.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 
 config("libyuv_config") {
   include_dirs = [
     ".",
     "include",
   ]
 }
 
 use_neon = current_cpu == "arm64" || (current_cpu == "arm" && (arm_use_neon || arm_optionally_use_neon))
 
-source_set("libyuv") {
+static_library("libyuv") {
   sources = [
     # Headers
     "include/libyuv.h",
     "include/libyuv/basic_types.h",
     "include/libyuv/compare.h",
     "include/libyuv/convert.h",
     "include/libyuv/convert_argb.h",
     "include/libyuv/convert_from.h",
     "include/libyuv/convert_from_argb.h",
     "include/libyuv/cpu_id.h",
@@ skipping 85 matching lines @@
     ]
 
     public_configs = [ ":libyuv_config" ]
 
     if (current_cpu != "arm64") {
       configs -= [ "//build/config/compiler:compiler_arm_fpu" ]
       cflags = [ "-mfpu=neon" ]
     }
   }
 }