About findFXC

I find that if we change the default windows kits installation path,the function can't work correctly.
I think we can search from system environment variables.
Or we can let the user manually set a fxcpath string.

ShaderGen/src/ShaderGen.App/Program.cs

Lines 585 to 599 in badb819

	private static string FindFxcExe()
	{
	const string WindowsKitsFolder = @"C:\Program Files (x86)\Windows Kits";
	if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows) && Directory.Exists(WindowsKitsFolder))
	{
	IEnumerable<string> paths = Directory.EnumerateFiles(
	WindowsKitsFolder,
	"fxc.exe",
	SearchOption.AllDirectories);
	string path = paths.FirstOrDefault(s => !s.Contains("arm"));
	return path;
	}
	return null;
	}