[Clang] Fix compilation with GCC 7.5

Fixes #73628

Author: cor3ntin

clang/lib/Sema/SemaDeclCXX.cpp

@@ -17299,7 +17299,7 @@ bool Sema::EvaluateStaticAssertMessageAsString(Expr *Message,
                                     OverloadCandidateSet::CSK_Normal);
     if (MemberLookup.empty())
       return std::nullopt;
-    return MemberLookup;
+    return std::move(MemberLookup);
   };
 
   bool SizeNotFound, DataNotFound;