DXC.EXE lacks support for long file paths

When long file paths are enabled on Windows 10 Version 1607 or later, DXC.EXE still fails to compile them.

In general the LLVM codebase supports very long file paths internally, so this is likely just a case of adding the following manifest to the binary.

<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0" xmlns:asmv3="urn:schemas-microsoft-com:asm.v3" >
    <asmv3:application>
        <asmv3:windowsSettings xmlns:ws2="http://schemas.microsoft.com/SMI/2016/WindowsSettings">
            <ws2:longPathAware>true</ws2:longPathAware>
        </asmv3:windowsSettings>
    </asmv3:application>
</assembly>

For example:

md "Projects\C++\this is a rather long path for a path on windows where long paths are a problem with the limit of two hundred fifty characters but there is a solution which implies adding a registry key and configuring the project to include a manifest"
// copy PixelShader.hlsl to this new folder
dxc /T ps_6_0 "Projects\C++\this is a rather long path for a path on windows where long paths are a problem with the limit of two hundred fifty characters but there is a solution which implies adding a registry key and configuring the project to include a manifest\PixelShader.hlsl"
The system cannot find the path specified. Projects\C++\this is a rather long path for a path on windows where long paths are a problem with the limit of two hundred fifty characters but there is a solution which implies adding a registry key and configuring the project to include a manifest\PixelShader.hlsl

No source file or test is named. Start by locating the Windows build configuration for DXC.EXE and reproduce the reported long-path command on Windows 10 version 1607 or later. Done means DXC.EXE can compile the HLSL file from a path exceeding the usual Windows limit when long paths are enabled.