This cl contains the necessary config and build changes
to make SwiftShader work on Fuchsia x64.

Passes all tests in content_unittests.

Bug: chromium:739182

Change-Id: I7df44bd6b12b2560f18e4375f16ada3850f1d8a5
Reviewed-on: https://swiftshader-review.googlesource.com/20208Reviewed-by: Alexis Hétu <sugoi@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>