In preparation for updating DIL to handle assignments, this adds a
member variable to the DIL Interpreter indicating whether or not
updating program variables is allowed. For invocations from the LLDB
command prompt (through "frame variable") we want to allow it, but from
other places we might not. Therefore we also add new StackFrame
ExpressionPathOption, eExpressionPathOptionsAllowVarUpdates, which we
add to calls from CommandObjectFrame, and which is checked in
GetValueForVariableExpressionPath. Finally, we also add a parameter,
can_update_vars, with a default value of true, to
ValueObject::SetValueFromInteger, as that will be the main function used
to by assignment in DIL.
f43ee18e98