Fuchsia has no mallinfo() or getrusage(). This silences the build
warnings.

Bug: chromium:921807
Change-Id: Ifbb274efdc99ebdf38a6b6b8760ffd42be6fafa4
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/31708Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Fabrice de Gans-Riberi <fdegans@chromium.org>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>