DX Compiler release for July 2019

DXC release for July 2019. (some files were rebuilt since then with different dates) Contains dxc.exe, dxcompiler.dll, and corresponding lib and header. Also validator DLL dxil.dll from 19H1 OS drop.

v1.2.0-alpha

This release contains everything up to Shader Model 6.1 as well as a preview of Shader Model 6.2