For now, this has to be enabled manually using
TriangleBenchmark::multisample

Bug: b/158231104
Change-Id: I929da4bf72e6f354aeb089e19fdd6a749f839d3f
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/45689
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>