[DWARF] - Provide default implementations for methods of LoadedObjectInfo

[grimar]

Summary

It is a bit unconvinent that client should implement stubs for these two methods
on its side even if not use them at all.

For example in D35005 I do not need them both, also there is one more
place in LLD where LoadedObjectInfo is used and have to implement stub clone()
method.

I suggest to provide default implementations.

[dblaikie]

getSectionLoadAddress seems fine - but I've fixed/improved the clone situation by generalizing a CRTP base helper in r307166, so you can probably use that in your other change

[grimar]

In D35009#799638, @dblaikie wrote:

but I've fixed/improved the clone situation by generalizing a CRTP base helper in r307166, so you can probably use that in your other change

Cool, thanks !

llvm/trunk/include/llvm/DebugInfo/DIContext.h

public:
 
   /// Obtain the Load Address of a section by SectionRef.
   ///
   /// Calculate the address of the given section.
   /// The section need not be present in the local address space. The addresses
   /// need to be consistent with the addresses used to query the DIContext and
   /// the output of this function should be deterministic, i.e. repeated calls with
   /// the same Sec should give the same address.
-  virtual uint64_t getSectionLoadAddress(const object::SectionRef &Sec) const = 0;
+  virtual uint64_t getSectionLoadAddress(const object::SectionRef &Sec) const {
+    return 0;
+  }
 
   /// If conveniently available, return the content of the given Section.
   ///
   /// When the section is available in the local address space, in relocated (loaded)
   /// form, e.g. because it was relocated by a JIT for execution, this function
   /// should provide the contents of said section in `Data`. If the loaded section
   /// is not available, or the cost of retrieving it would be prohibitive, this
   /// function should return false. In that case, relocations will be read from the