Can't build with Visual Studio 2015 SP3

[SampsonChing]

To viewer,
I have downloaded the source from this site. I followed the instruction to create openSSL.sln and project files everything was fine.
I use Visual Studio Profession 2015 Version 14.0.25431.01 Update 3 to open openSSL.sln and build "NT-Phone-8.1-Static-Unicode(Windows Phone 8.1)". First, I got error:"fatal error C1107 can't find Windows.winmd", I find a Windows.winmd and copy it to proper folder, problem solved. And then, build it again. This time I got another error message "error C3624: 'System::Attribute': use of this type requires a reference to assembly 'mscorlib'", What can I do to fix this problem?