Cherry-pick upstream r238083
[Sema] Don't use dyn_cast to detect an AtomicType

An AtomicType might be hidden behind arbitrary levels of typedefs.
getAs<> will reliably walk through the sugar to get the underlying
AtomicType.

This fixes PR23638.

R=jfb@chromium.org
BUG= https://code.google.com/p/nativeclient/issues/detail?id=4228

Review URL: https://codereview.chromium.org/1238843002 .
2 files changed