We need to keep a copy of the CPU features for 'mattrs' so they don't
get deleted before we pass them into rr::resolveExternalSymbol() by
raw pointer.

Bug: b/139412871
Change-Id: Iedc2d05fe3ec0d903ffa283994ad95a9cd993e22
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/40732
Presubmit-Ready: Nicolas Capens <nicolascapens@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>