Convert third_party source sets to static libraries.

third_party/iccjpeg/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.
 
 config("iccjpeg_config") {
   include_dirs = [ "." ]
 }
 
-source_set("iccjpeg") {
+static_library("iccjpeg") {
   sources = [
     "iccjpeg.c",
     "iccjpeg.h",
   ]
 
   public_configs = [ ":iccjpeg_config" ]
   deps = [
     "//third_party:jpeg",
   ]
 }