Fix bitcode upgrade for DIGlobalVariables with a var: field.

This is a follow-up to https://reviews.llvm.org/D29349.  It turns out
that NeedUpgradeToDIGlobalVariableExpression is always necessary when
we encountered a version==0 record because it may always be referenced
via a list of globals in a DICompileUnit. My tests weren't good enough
to catch this though. To trigger this case, we need much older bitcode
produced by LLVM around version 3.7.

<rdar://problem/30404262>

Differential Revision: https://reviews.llvm.org/D29693

llvm-svn: 294488

llvm/lib/Bitcode/Reader/MetadataLoader.cpp

@@ -1437,6 +1437,7 @@ Error MetadataLoader::MetadataLoaderImpl::parseOneMetadata(
     } else if (Version == 0) {
       // Upgrade old metadata, which stored a global variable reference or a
       // ConstantInt here.
+      NeedUpgradeToDIGlobalVariableExpression = true;
       Metadata *Expr = getMDOrNull(Record[9]);
       uint32_t AlignInBits = 0;
       if (Record.size() > 11) {
@@ -1467,8 +1468,6 @@ Error MetadataLoader::MetadataLoaderImpl::parseOneMetadata(
       DIGlobalVariableExpression *DGVE = nullptr;
       if (Attach || Expr)
         DGVE = DIGlobalVariableExpression::getDistinct(Context, DGV, Expr);
-      else
-        NeedUpgradeToDIGlobalVariableExpression = true;
       if (Attach)
         Attach->addDebugInfo(DGVE);