Made sure both LLVM and Subzero has the /src directory in their
include directory list. Removed unused ../ in front of "Common"
includes as a cleanup.

Change-Id: Ib4a6fb772fa03a9a3cad82594db1b1650007e47f
Reviewed-on: https://swiftshader-review.googlesource.com/20728Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>