Revert "Revert r189902 as the workaround shouldn't be necessary anymore."

Needs testcase updates.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190000 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 535b094..6835f40 100644
--- a/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -161,8 +161,12 @@
 /// Return Dwarf Version by checking module flags.
 static unsigned getDwarfVersionFromModule(const Module *M) {
   Value *Val = M->getModuleFlag("Dwarf Version");
+  // If we don't have a value in the module go ahead and use the default in
+  // dwarf::DWARF_VERSION.
+  // FIXME: Apple ld has a problem parsing compilation units that specify a
+  // dwarf version of greater than 3.
   if (!Val)
-    return dwarf::DWARF_VERSION;
+    return Triple(M->getTargetTriple()).isOSDarwin() ? 3 : dwarf::DWARF_VERSION;
   return cast<ConstantInt>(Val)->getZExtValue();
 }