Reland r200340 - 'Add line table debug info to COFF files when using a win32 triple'

This incorporates a couple of fixes reviewed at http://llvm-reviews.chandlerc.com/D2651

llvm-svn: 200440
diff --git a/llvm/lib/MC/MCObjectFileInfo.cpp b/llvm/lib/MC/MCObjectFileInfo.cpp
index 796d03b..a160f29 100644
--- a/llvm/lib/MC/MCObjectFileInfo.cpp
+++ b/llvm/lib/MC/MCObjectFileInfo.cpp
@@ -150,6 +150,8 @@
   LSDASection = Ctx->getMachOSection("__TEXT", "__gcc_except_tab", 0,
                                      SectionKind::getReadOnlyWithRel());
 
+  COFFDebugSymbolsSection = 0;
+
   if (T.isMacOSX() && !T.isMacOSXVersionLT(10, 6)) {
     CompactUnwindSection =
       Ctx->getMachOSection("__LD", "__compact_unwind",
@@ -458,6 +460,8 @@
                        ELF::SHF_ALLOC,
                        SectionKind::getReadOnly());
 
+  COFFDebugSymbolsSection = 0;
+
   // Debug Info Sections.
   DwarfAbbrevSection =
     Ctx->getELFSection(".debug_abbrev", ELF::SHT_PROGBITS, 0,