This helps clarify dependencies and simplifies include paths.

Bug swiftshader:86

Change-Id: I564ee420bb9029fa6428e49b63a86d633301bec2
Reviewed-on: https://swiftshader-review.googlesource.com/13288Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>