The copy constructor of std::atomic is not allowed, so initialization
through operator= is not allowed. Explicitly using the AtomicInt
constructor to fix this issue.

Change-Id: If77763e89e0d958d8a4b5a83d5d7bd9e3ba08ff6
Reviewed-on: https://swiftshader-review.googlesource.com/12508Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>