Don't copy entire value into m_data unless we need to. If we did this and the entire variable failed to be read, we wouldn't be able to display any actual values that were in good memory.  This will also make things more efficient by not have every struct/union/class/array copy its entire value into a ValueObject.m_data even though no one was using it.
Make the use of DW_AT_ranges in the compile unit depend also upon
the existence of comdat/special sections.