[LLDB] Set the right address size on output DataExtractors from ObjectFile

If filling in a DataExtractor from an ObjectFile, e.g. via the
ReadSectionData method, the output DataExtractor gets the address
size from the m_data member.

ObjectFile's m_data member is initialized without knowledge about
the address size (so the address size is set based on the host's
sizeof(void*), and at that point within ObjectFile's constructor,
virtual methods implemented in subclasses (like GetAddressByteSize())
can't be called, therefore fix it up when filling in external
DataExtractors.

This makes sure that line tables from executables with a different
address size are parsed properly; previously this tripped up
DWARFDebugLine::LineTable::parse for 32 bit executables on a 64 bit
host, as the address size in the line table (4) didn't match the
one set in the DWARFDataExtractor.

Differential Revision: https://reviews.llvm.org/D70848