Added chached items in symbol to the things that are walked by the GC

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Need to export g++-4.8 as compiler name

And we do not need those libraries.

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Added assert to make sure forward pointers are not lost during GC

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Introduce MarkObjectAsInvalid for debugging GC issues

Objects are only invalidated when assertions are enabled i.e. #ifndef NDEBUG

Signed-off-by: Stefan Marr <git@stefan-marr.de>