Fixed bug (compile issue) introduced with previous refactor.

Critical sections need to be defined whenever atomics are not
natively supported. Fixed wrong ifdef.

Change-Id: Icd5e2245a65c6832c52ab1ba07cf9d9b89768859
Merge topic 'atomic-compile-error-win32' into master

031fdf7e Fixed bug (compile issue) introduced with previous refactor.