Remove unused DwarfSectionOffsetDirective string

The value isn't actually used, and setting it emits a COFF specific
directive.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180064 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/AsmPrinter/AsmPrinterDwarf.cpp b/lib/CodeGen/AsmPrinter/AsmPrinterDwarf.cpp
index 156acac..31e42d4 100644
--- a/lib/CodeGen/AsmPrinter/AsmPrinterDwarf.cpp
+++ b/lib/CodeGen/AsmPrinter/AsmPrinterDwarf.cpp
@@ -141,7 +141,7 @@
 void AsmPrinter::EmitSectionOffset(const MCSymbol *Label,
                                    const MCSymbol *SectionLabel) const {
   // On COFF targets, we have to emit the special .secrel32 directive.
-  if (MAI->getDwarfSectionOffsetDirective()) {
+  if (MAI->needsDwarfSectionOffsetDirective()) {
     OutStreamer.EmitCOFFSecRel32(Label);
     return;
   }