Add basic fission support to SymbolFileDWARF

* Create new dwo symbol file class
* Add handling for .dwo sections
* Change indexes in SymbolFileDWARF to store compile unit offset next to
  DIE offset
* Propagate queries from dwarf compile unit to the dwo compile unit
  where applicable

Differential revision: http://reviews.llvm.org/D12291

llvm-svn: 247132
diff --git a/lldb/source/Symbol/ObjectFile.cpp b/lldb/source/Symbol/ObjectFile.cpp
index 804662f..b61d499 100644
--- a/lldb/source/Symbol/ObjectFile.cpp
+++ b/lldb/source/Symbol/ObjectFile.cpp
@@ -602,15 +602,23 @@
 }
 
 SectionList *
-ObjectFile::GetSectionList()
+ObjectFile::GetSectionList(bool update_module_section_list)
 {
     if (m_sections_ap.get() == nullptr)
     {
-        ModuleSP module_sp(GetModule());
-        if (module_sp)
+        if (update_module_section_list)
         {
-            lldb_private::Mutex::Locker locker(module_sp->GetMutex());
-            CreateSections(*module_sp->GetUnifiedSectionList());
+            ModuleSP module_sp(GetModule());
+            if (module_sp)
+            {
+                lldb_private::Mutex::Locker locker(module_sp->GetMutex());
+                CreateSections(*module_sp->GetUnifiedSectionList());
+            }
+        }
+        else
+        {
+            SectionList unified_section_list;
+            CreateSections(unified_section_list);
         }
     }
     return m_sections_ap.get();