switch bigint to a static_library

third_party/BUILD.gn

 # Copyright 2014 PDFium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 group("third_party") {
   deps = [
     ":bigint",
     ":fx_freetype",
     ":pdfium_base",
   ]
 }
 
-source_set("bigint") {
+static_library("bigint") {
   configs -= [ "//build/config/compiler:chromium_code" ]
   configs += [
     "//build/config/compiler:no_chromium_code",
     "//third_party/pdfium:pdfium_config",
   ]
   sources = [
     "bigint/BigInteger.cc",
     "bigint/BigInteger.hh",
     "bigint/BigIntegerLibrary.hh",
     "bigint/BigIntegerUtils.cc",
@@ skipping 281 matching lines @@
     "base/macros.h",
     "base/nonstd_unique_ptr.h",
     "base/numerics/safe_conversions.h",
     "base/numerics/safe_conversions_impl.h",
     "base/numerics/safe_math.h",
     "base/numerics/safe_math_impl.h",
     "base/stl_util.h",
     "base/template_util.h",
   ]
 }