Update llpc from commit: fab733c5
Update llpc from commit: fab733c5

It fix the build error without spvgen. Add an option to control if
enable lit test.

GPUOpen-Drivers/llpc,googlestadia/llpc,googlestadia/llpc,googlestadia/llpc,googlestadia/llpc,googlestadia/llpc,GPUOpen-Drivers/llpc,GPUOpen-Drivers/llpc,GPUOpen-Drivers/llpc,GPUOpen-Drivers/llpc