Encapsulate the DWARF string pool in a separate type.

Pulls out some more code from some of the rather monolithic DWARF
classes. Unlike the address table, the string table won't move up into
DwarfDebug - each DWARF file has its own string table (but there can be
only one address table).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207277 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/AsmPrinter/DwarfAccelTable.cpp

@@ -179,8 +179,8 @@ void DwarfAccelTable::EmitData(AsmPrinter *Asm, DwarfFile *D) {
       // Remember to emit the label for our offset.
       Asm->OutStreamer.EmitLabel((*HI)->Sym);
       Asm->OutStreamer.AddComment((*HI)->Str);
-      Asm->EmitSectionOffset(D->getStringPoolEntry((*HI)->Str),
-                             D->getStringPoolSym());
+      Asm->EmitSectionOffset(D->getStringPool().getSymbol(*Asm, (*HI)->Str),
+                             D->getStringPool().getSectionSymbol());
       Asm->OutStreamer.AddComment("Num DIEs");
       Asm->EmitInt32((*HI)->Data.size());
       for (ArrayRef<HashDataContents *>::const_iterator