Adapt to GlueGen commit 2f6586292cd298bbc19d8acda0f7cf303c82078b (compount call-by-value extension)

- GLU*: initializeImpl() is no more required, since it's not forced .. uncomment in manual static initializer
- GLX: 'ForceStaticInitCode GLX', i.e. forcing native code, as used in our manual implementation.