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: Id25dd986a888af5175d43c33e4c60bb3e4733eda
Reviewed-on: https://swiftshader-review.googlesource.com/c/22128Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>