[DWARF] Emit a split line table only if there are split type units.

A .debug_info.dwo section doesn't use the .debug_line.dwo section.

llvm-svn: 326395
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index a9aa00c..3a75530 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -2105,6 +2105,8 @@
 
 void DwarfDebug::emitDebugLineDWO() {
   assert(useSplitDwarf() && "No split dwarf?");
+  if (!HasSplitTypeUnits)
+    return;
   Asm->OutStreamer->SwitchSection(
       Asm->getObjFileLowering().getDwarfLineDWOSection());
   SplitTypeUnitFileTable.Emit(*Asm->OutStreamer, MCDwarfLineTableParams());
@@ -2220,6 +2222,7 @@
       InfoHolder.computeSizeAndOffsetsForUnit(TU.first.get());
       InfoHolder.emitUnit(TU.first.get(), useSplitDwarf());
     }
+    HasSplitTypeUnits = useSplitDwarf();
   }
   CU.addDIETypeSignature(RefDie, Signature);
 }