Windows 7 not supported

[Markyparky56]

This is sort of a non-issue with Windows 7 going End-of-life within a year.

Due to the use of EnterSynchronizationBarrier and friends the minimum supported Windows version is Windows 8, according to Microsoft Dev Center.

Attempting to run Tests.FrameGraph.exe on Windows 7 errors out at start up with an "Entry Point Not Found" popup, relating to `EnterSynchronizatonBarrier" not being found in KERNERL32.dll.

[azhirnov]

There are some alternative implementations for the barrier.
I added check for target sdk version to enable win8 version.

[clojur]

Cmake is OK, but a lot of errors were reported during compilation.
such as
[ error C2514: “std::shared_lock”:Class has no constructor (compile source files G:\FrameGraph\tests\framegraph\ImplTests\ImplTest_Scene1.cpp) ]