[COFF] Adjust how we flag weak externals

This fixes PR36096.

Originally based on a patch by Martell Malone.

Differential Revision: https://reviews.llvm.org/D44357

llvm-svn: 337613
diff --git a/llvm/lib/Object/ArchiveWriter.cpp b/llvm/lib/Object/ArchiveWriter.cpp
index c979673..ea17b22 100644
--- a/llvm/lib/Object/ArchiveWriter.cpp
+++ b/llvm/lib/Object/ArchiveWriter.cpp
@@ -294,8 +294,7 @@
     return false;
   if (!(Symflags & object::SymbolRef::SF_Global))
     return false;
-  if (Symflags & object::SymbolRef::SF_Undefined &&
-      !(Symflags & object::SymbolRef::SF_Indirect))
+  if (Symflags & object::SymbolRef::SF_Undefined)
     return false;
   return true;
 }