ShaderCache: Add a data version field

We can increment this to prevent people's shader caches from growing too
large with shader changes.

src/core/CMakeLists.txt

@@ -84,6 +84,7 @@ add_library(core
     save_state_version.h
     settings.cpp
     settings.h
+    shader_cache_version.h
     shadergen.cpp
     shadergen.h
     sio.cpp