First version of Chromium build files for SwiftShader.
Works for Linux only at this point.
Other platforms are there, but untested at the moment.

Change-Id: I8f389db9937feda74c7009cf7a22938dab9e69d5
Reviewed-on: https://swiftshader-review.googlesource.com/5520Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>