[MERGE #5682 @duongnhn] fixes #5681 avoid c2440 error lose const qualifier

Merge pull request #5682 from duongnhn:user/duongn/c2440-lose-const-qualifier

When /Zc:strictStrings is enable, encounter this error https://msdn.microsoft.com/en-us/library/dn449508.aspx since we cast literal string to non-const char pointer.

Author: duongnhn

bin/NativeTests/BigUIntTest.cpp

@@ -226,7 +226,7 @@ namespace BigUIntTest
     TEST_CASE("Init_From_Char_Of_Digits", "[BigUIntTest]")
     {
         BigUInt biDec;
-        char *charDigit;
+        const char *charDigit;
         bool result;
         int charDigitLength;