Introduce TraceResolver::load_addresses() for raw address array

[Gerold103]

TraceResolver has a load_stacktrace() method accepting only an
object like StackTrace. That object is basically an array of
pointers.

This was not really convenient, because

1. it required carrying of this StackTrace object from the moment
   of its creation to the load_stacktrace() invocation. Sometimes
   this is a long path. And that may break encapsulation, if a
   project, using Backward, does not want to include Backward
   header anywhere except for 1 or 2 C++ files, responsible for
   collection and resolution of addresses. So basically,
   load_stacktrace() prevented split of stack load and stack
   resolution into separate submodules of a project;

2. that made impossible to use Backward to resolve a stack,
   collected not via Backward.

The patch introduces a new method load_addresses(), accepting an
array of addresses. That solves both problems.

Alongside, to avoid increase of code duplication by empty
load_addresses() methods in the classes where they are not needed,
now both load_stacktrace() and load_addresses() are in one base
class, used by all resolvers. load_addresses() is a virtual
method, which does nothing, except for a couple of classes, where
it is overridden as backtrace_symbols(). load_stacktrace() just
calls load_addresses() and doesn't need to be defined everywhere
again and again.

[Gerold103]

Any chances on getting this merged someday?

[Gerold103]

Any chances on getting this merged someday?

[Gerold103]

@bombela ping, what can be done to speed up the review and merge?

[Gerold103]

@bombela ping, what can be done to speed up the review and merge?

[bombela]

Sorry, I kept pushing back.

Does the code still work on C++98? I see the use of override which I think was introduced in C++11?

[Gerold103]

Hm. I didn't check, but I see it is used in the master branch too. I assumed it is ok to use it then.

[bombela]

Ahah indeed, there is a macro making it a no-op!

[Gerold103]

Great, thanks for the merge!