This change requires include directives to include the Vulkan/ path so
it's clearer when we have dependencies across layers/folders.

This was already the case for the other build files, so it avoids
build breakage as well.

Bug b/126557661

Change-Id: I4d8773e8c28e6677fd1e93ca9c9d2d843431343c
Reviewed-on: https://swiftshader-review.googlesource.com/c/25948Reviewed-by: Alexis Hétu <sugoi@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>