qt5: tests: Make sure static plugin symbols are pulled in

Since we're now properly linking against static plugins for qt binaries,
we need to ensure that they're Imported properly.

Without these Imports, the linker drops some of the unused linked libs, causing
undefined symbols in QtCore.

src/qt/test/test_main.cpp

@@ -1,3 +1,4 @@
+#include "bitcoin-config.h"
 #include "paymentservertests.h"
 #include "uritests.h"
 
@@ -5,6 +6,14 @@
 #include <QObject>
 #include <QTest>
 
+#if defined(QT_STATICPLUGIN) && QT_VERSION < 0x050000
+#include <QtPlugin>
+Q_IMPORT_PLUGIN(qcncodecs)
+Q_IMPORT_PLUGIN(qjpcodecs)
+Q_IMPORT_PLUGIN(qtwcodecs)
+Q_IMPORT_PLUGIN(qkrcodecs)
+#endif
+
 // This is all you need to run all the tests
 int main(int argc, char *argv[])
 {