Speculatively fix Clang build bots

This is intended to address the issues found in:
https://lab.llvm.org/buildbot/#/builders/192/builds/3337
https://lab.llvm.org/buildbot/#/builders/124/builds/7968

Author: AaronBallman

clang/lib/Sema/SemaDeclCXX.cpp

@@ -16925,7 +16925,7 @@ bool Sema::EvaluateStaticAssertMessageAsString(Expr *Message,
     OverloadCandidateSet::iterator Best;
     switch (Candidates.BestViableFunction(*this, Loc, Best)) {
     case OR_Success:
-      return MemberLookup;
+      return std::move(MemberLookup);
     default:
       if (Diag)
         Candidates.NoteCandidates(