Fix GLX backend in static builds

Do not attempt to resolve dynamically in static builds. This is not
wrong, but if the GL library is statically linked just like the rest
of Qt, it won't work. Therefore just call the function directly in static
builds, it should be no problem on modern systems.

Task-number: QTBUG-46499
Change-Id: I35fd7c3b5b180d753becbb57377b27dd1a8747ad
Reviewed-by: Andy Shaw <andy.shaw@theqtcompany.com>
Reviewed-by: Jørgen Lind <jorgen.lind@theqtcompany.com>

src/plugins/platforms/xcb/gl_integrations/xcb_glx/qglxintegration.cpp

@@ -540,6 +540,9 @@ void QGLXContext::swapBuffers(QPlatformSurface *surface)
 
 void (*QGLXContext::getProcAddress(const QByteArray &procName)) ()
 {
+#ifdef QT_STATIC
+    return glXGetProcAddressARB(reinterpret_cast<const GLubyte *>(procName.constData()));
+#else
     typedef void *(*qt_glXGetProcAddressARB)(const GLubyte *);
     static qt_glXGetProcAddressARB glXGetProcAddressARB = 0;
     static bool resolved = false;
@@ -569,6 +572,7 @@ void (*QGLXContext::getProcAddress(const QByteArray &procName)) ()
     if (!glXGetProcAddressARB)
         return 0;
     return (void (*)())glXGetProcAddressARB(reinterpret_cast<const GLubyte *>(procName.constData()));
+#endif
 }
 
 QSurfaceFormat QGLXContext::format() const