Expand `auto` whose real type is not obvious from context.

llvm-svn: 248876
diff --git a/lld/ELF/InputFiles.cpp b/lld/ELF/InputFiles.cpp
index ebd666e..dc39c1d 100644
--- a/lld/ELF/InputFiles.cpp
+++ b/lld/ELF/InputFiles.cpp
@@ -181,7 +181,7 @@
 }
 
 void ArchiveFile::parse() {
-  auto ArchiveOrErr = Archive::create(MB);
+  ErrorOr<std::unique_ptr<Archive>> ArchiveOrErr = Archive::create(MB);
   error(ArchiveOrErr, "Failed to parse archive");
   File = std::move(*ArchiveOrErr);