qpluginloader: fix static build (on iOS)

Since the function locatePlugin is unused when
building Qt statically, the build fails on
iOS. This patch will ensure that we only define it
for shared builds.

Change-Id: Idf3c3246d3cac94a3c001cc261f326e9a396aa31
Reviewed-by: David Faure <david.faure@kdab.com>

src/corelib/plugin/qpluginloader.cpp

@@ -278,6 +278,7 @@ bool QPluginLoader::isLoaded() const
     return d && d->pHnd && d->instance;
 }
 
+#if defined(QT_SHARED)
 static QString locatePlugin(const QString& fileName)
 {
     QStringList prefixes = QLibraryPrivate::prefixes_sys();
@@ -309,6 +310,7 @@ static QString locatePlugin(const QString& fileName)
         qDebug() << fileName << "not found";
     return QString();
 }
+#endif
 
 /*!
     \property QPluginLoader::fileName