update cmake: Simplify PythonQt_QtAll reusing PYTHONQT_EXPORT export macro

Author: jamesobutler

extensions/PythonQt_QtAll/PythonQt_QtAll.h

@@ -33,11 +33,26 @@
  *
  */
 
-#include "PythonQtSystem.h" // For PYTHONQT_EXPORT
+// Export macro for the PythonQt_QtAll shared library.
+// When building the DLL, PYTHONQT_QTALL_EXPORTS is defined by the build system;
+// consumers of the DLL get __declspec(dllimport) / default visibility instead.
+#if defined(WIN32)
+  #ifdef PYTHONQT_QTALL_EXPORTS
+    #define PYTHONQT_QTALL_EXPORT __declspec(dllexport)
+  #else
+    #define PYTHONQT_QTALL_EXPORT __declspec(dllimport)
+  #endif
+#else
+  #ifdef PYTHONQT_QTALL_EXPORTS
+    #define PYTHONQT_QTALL_EXPORT __attribute__((__visibility__("default")))
+  #else
+    #define PYTHONQT_QTALL_EXPORT
+  #endif
+#endif
 
 namespace PythonQt_QtAll {
 //! Initialize the Qt bindings enabled at configuration time
-PYTHONQT_EXPORT void init();
+PYTHONQT_QTALL_EXPORT void init();
 }
 
 #endif