CMake: don't treat Q_CORE_EXPORT special

Let CMake create a qtcoreexports.h just like for every other Qt
library, include it in a fitting place in qglobal.h. Currently, that's
in the middle of the file, but that will be cleaned up in subsequent
commits.

Task-number: QTBUG-99313
Change-Id: I3ea9f4772b0ad63c7e8431689146cac3336c5ccf
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>
Reviewed-by: Alexey Edelev <alexey.edelev@qt.io>

src/corelib/CMakeLists.txt

@@ -266,6 +266,7 @@ qt_internal_add_module(Core
         Qt::GlobalConfigPrivate # special case
     PRECOMPILED_HEADER
         "global/qt_pch.h"
+    GENERATE_CPP_EXPORTS
     PUBLIC_LIBRARIES  # special case:
         Qt::Platform # special case:
     # special case begin

src/corelib/global/qglobal.h

@@ -516,15 +516,12 @@ constexpr inline Deprecated_t Deprecated = {};
 #  ifndef QT_SHARED
 #    define QT_SHARED
 #  endif
-#  if defined(QT_BUILD_CORE_LIB)
-#    define Q_CORE_EXPORT Q_DECL_EXPORT
-#  else
-#    define Q_CORE_EXPORT Q_DECL_IMPORT
-#  endif
-#else
-#  define Q_CORE_EXPORT
 #endif
 
+QT_BEGIN_INCLUDE_NAMESPACE
+#include <QtCore/qtcoreexports.h>
+QT_END_INCLUDE_NAMESPACE
+
 /*
    Some classes do not permit copies to be made of an object. These
    classes contains a private copy constructor and assignment