Modify big integer library

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 5d0210ff34635299ee90b98bf201ac6897ae0282..2e471637d49a3f67c727aebf1fefd0435d648edb 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -90,6 +90,7 @@ static_library("pdfium") {
 
   deps = [
     ":safemath",
+    ":bigint",
     ":fdrm",
     ":formfiller",
     ":fpdfapi",
@@ -128,6 +129,21 @@ component("safemath") {
   ]
 }
 
+static_library("bigint") {
+  sources = [
+    "third_party/bigint/BigInteger.hh",
+    "third_party/bigint/BigIntegerLibrary.hh",
+    "third_party/bigint/BigIntegerUtils.hh",
+    "third_party/bigint/BigUnsigned.hh",
+    "third_party/bigint/NumberlikeArray.hh",
+    "third_party/bigint/BigUnsignedInABase.hh",
+    "third_party/bigint/BigInteger.cc",
+    "third_party/bigint/BigIntegerUtils.cc",
+    "third_party/bigint/BigUnsigned.cc",
+    "third_party/bigint/BigUnsignedInABase.cc",
+  ]
+}
+
 static_library("fdrm") {
   sources = [
     "core/include/fdrm/fx_crypt.h",