VBS Enclave SDK 0.1.2.1 (PreRelease)

Patches the veil_enclave_lib project so it can be built via vcpkg. No new nuget package has now been created as this is just an update to the project file.

Nuget package link:
https://www.nuget.org/packages/Microsoft.Windows.VBSEnclave.SDK

What's Changed

• Add /FS compiler flag to the veil_enclave_lib project by @bbonaby in #140

Full Changelog: sdk-v0.1.2-prerelease...sdk-v0.1.2.1-prerelease