Resubmitting 240466 after fixing the linux test suite failures.

A few extras were fixed

- Symbol::GetAddress() now returns an Address object, not a reference. There were places where people were accessing the address of a symbol when the symbol's value wasn't an address symbol. On MacOSX, undefined symbols have a value zero and some places where using the symbol's address and getting an absolute address of zero (since an Address object with no section and an m_offset whose value isn't LLDB_INVALID_ADDRESS is considered an absolute address). So fixing this required some changes to make sure people were getting what they expected. 
- Since some places want to access the address as a reference, I added a few new functions to symbol:
    Address &Symbol::GetAddressRef();
    const Address &Symbol::GetAddressRef() const;

Linux test suite passes just fine now.

<rdar://problem/21494354>

llvm-svn: 240702

lldb/source/Commands/CommandObjectSource.cpp

@@ -537,9 +537,9 @@ protected:
                 {
                     SymbolContext sc;
                     sc_list_symbols.GetContextAtIndex (i, sc);
-                    if (sc.symbol)
+                    if (sc.symbol && sc.symbol->ValueIsAddress())
                     {
-                        const Address &base_address = sc.symbol->GetAddress();
+                        const Address &base_address = sc.symbol->GetAddressRef();
                         Function *function = base_address.CalculateSymbolContextFunction();
                         if (function)
                         {