Added logging so we can see when we are trying to complete a forward type and...

Added logging so we can see when we are trying to complete a forward type and pull in the world. This is due to a compiler bug we are tracking (<rdar://problem/11291658>) where forward decls to classes and types are not properly scoped in namespaces, which results in the current LLDB looking for a type it will find many times in the accelerator tables, but never match. For example, when debugging with clang we get a forward decl like:

class AnalysisResolver;

And we will look for it everywhere and find many many matches, but the decl context of those matching DIEs is "clang::AnalysisResolver", so we never match anything, yet we pull in waaayyy too much DWARF in the process.

To enable this logging enable the "lookups" category in the "dwarf" log channel:

(lldb) log enable dwarf lookups

llvm-svn: 155233