[BOLT] Fix data race in shortenInstructions

[Amir]

Summary

Address ThreadSanitizer warning

[maksfb]

Not exactly an NFC since it's a fix, but I'm not sure if we can have a test case for a data race.

bolt/lib/Passes/BinaryPasses.cpp

for (MCInst &Inst : BB) {
       MCInst OriginalInst;
       if (opts::Verbosity > 2)
         OriginalInst = Inst;
 
       if (!BC.MIB->shortenInstruction(Inst, *BC.STI))
         continue;
 
       if (opts::Verbosity > 2) {
+        BC.scopeLock();
         outs() << "BOLT-INFO: shortening:\nBOLT-INFO:    ";
         BC.printInstruction(outs(), OriginalInst, 0, &Function);
         outs() << "BOLT-INFO: to:";
         BC.printInstruction(outs(), Inst, 0, &Function);
       }
 
       ++Count;
     }