Don't export QAtomicInt, it's all inline

Moreover, exporting it causes the horrible side-effect on Windows
(with MSVC) that the compiler will not inline the functions, but
instead will place indirect calls to the functions in QtCore DLL,
even in release mode. For such a critical piece of code, inlining
is necessary.

Change-Id: Ib31c12f6bf8dc8ece1b51824716a480559753c24
Reviewed-by: Marius Storm-Olsen <marius.storm-olsen@nokia.com>

src/corelib/thread/qatomic.h

@@ -57,7 +57,7 @@ QT_BEGIN_NAMESPACE
 #endif
 
 // High-level atomic integer operations
-class Q_CORE_EXPORT QAtomicInt : public QBasicAtomicInt
+class QAtomicInt : public QBasicAtomicInt
 {
 public:
     // Non-atomic API