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
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
index 4d3d22a..dafd389 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
@@ -7620,7 +7620,7 @@
                                     {
                                         if (exe_symbol->ValueIsAddress())
                                         {
-                                            const addr_t exe_file_addr = exe_symbol->GetAddress().GetFileAddress();
+                                            const addr_t exe_file_addr = exe_symbol->GetAddressRef().GetFileAddress();
                                             if (exe_file_addr != LLDB_INVALID_ADDRESS)
                                             {
                                                 if (location.Update_DW_OP_addr (exe_file_addr))