Also added the exports to allow enabling ES3 entirely on Linux.

Change-Id: Ia13d229b9ce1104a74a2bbd1f620296686cf18d4
Reviewed-on: https://swiftshader-review.googlesource.com/3064Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>