Reactor is a run-time code generator so it only needs to support the
CPU architecture for which it is being compiled. This reduces (static)
compile time and potentially the binary size.

Bug b/115344057

Change-Id: I925875e33e3c24dfc41abc1c055353a4099be618
Reviewed-on: https://swiftshader-review.googlesource.com/c/22208Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>