wasm: Export haveJspi() for dynamic linking

This symbol is required to be public in case of dynamic linking.
Mark it with Q_CORE_EXPORT.

Task-number: QTBUG-121839
Change-Id: Ie4b89532e39eb21f6efceefcceb922cd6d37983a
Reviewed-by: Even Oscar Andersen <even.oscar.andersen@qt.io>
Reviewed-by: Lorn Potter <lorn.potter@gmail.com>

src/corelib/platform/wasm/qstdweb_p.h

@@ -282,7 +282,7 @@ namespace qstdweb {
     }
 
     bool haveAsyncify();
-    bool haveJspi();
+    bool Q_CORE_EXPORT haveJspi();
     bool canBlockCallingThread();
 
     struct CancellationFlag