Use DefaultPlatformToolset if available

[noloader]

• DefaultPlatformToolset will avoid the project upgrade wizard when opening under most modern versions of Visual Studio.

• Switch to UTF-8 encoding without Byte Order Mark (BOM)

[daniel-dinu]

While your changes suppress the project upgrade wizard, they can introduce errors:
Error MSB8036 The Windows SDK version 8.1 was not found. Install the required version of Windows SDK or change the SDK version in the project property pages or by right-clicking the solution and selecting "Retarget solution".
I could not find a way to fix these errors in the project files.

[noloader]

Error MSB8036 The Windows SDK version 8.1 was not found.

I could not find a way to fix these errors in the project files.

Open the vcxproj file in a text editor. Delete the line with <WindowsTargetPlatformVersion>8.1</WindowsTargetPlatformVersion>. WindowsTargetPlatformVersion came along later. We don't even use it in Crypto++. See, for example, cryptlib.vcxproj.

I think the change also needed Commit 79f5b4c7. It dropped the toolchain version back down to VS2010 from VS2012 or VS2013.

Let me update the pull request. If you still have problems close this PR and I won't trouble you again.

[daniel-dinu]

When I said I could not find a way to fix these errors in the project files, I was referring to a way that does not involve an edit by the user of the configuration using the interface or directly in the vcxproj file.

Removing WindowsTargetPlatformVersion from the vcxproj file does not solve the problem. I get the same error with cryptopp.

If this error can not be fixed, I would keep the project update wizard rather than requiring users to fix the error.