Access library dependencies through a single object.

Bug 18752589

Change-Id: I93155cead50b30faa876023f9ed00f60b7c9e34e
Reviewed-on: https://swiftshader-review.googlesource.com/2831
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Greg Hartman <ghartman@google.com>
Tested-by: Greg Hartman <ghartman@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>