[CodeGen] Fix invalid DWARF info on Win64

The relocations for `DIEEntry::EmitValue` were wrong for Win64
(emitting FK_Data_4 instead of FK_SecRel_4). This corrects that
oversight so that the DWARF data is correct in Win64 COFF files.

Fixes PR15393.

Patch by Jameson Nash <jameson@juliacomputing.com> based on a patch
by David Majnemer.

Differential Revision: https://reviews.llvm.org/D21731

llvm-svn: 289013
diff --git a/llvm/lib/MC/MCCodeView.cpp b/llvm/lib/MC/MCCodeView.cpp
index ac1acc0..ae0e50a 100644
--- a/llvm/lib/MC/MCCodeView.cpp
+++ b/llvm/lib/MC/MCCodeView.cpp
@@ -200,7 +200,7 @@
   OS.EmitIntValue(unsigned(ModuleSubstreamKind::Lines), 4);
   OS.emitAbsoluteSymbolDiff(LineEnd, LineBegin, 4);
   OS.EmitLabel(LineBegin);
-  OS.EmitCOFFSecRel32(FuncBegin);
+  OS.EmitCOFFSecRel32(FuncBegin, /*Offset=*/0);
   OS.EmitCOFFSectionIndex(FuncBegin);
 
   // Actual line info.