[BOLT][AArch64] add lock to FixRelaxations pass

[treapster]

Summary

Since the pass is multithreaded, BC.Ctx must be protected. Otherwise we get crashes when processing.

[yota9]

Thanks

bolt/lib/Passes/FixRelaxationPass.cpp

for (auto II = BB.begin(); II != BB.end(); ++II) {
       const MCInst &Add = *NextII;
       if (!BC.MIB->matchAdrpAddPair(Adrp, Add))
         continue;
 
       const MCSymbol *Symbol = BC.MIB->getTargetSymbol(Add);
       if (!Symbol || AdrpSymbol == Symbol)
         continue;
 
+      auto L = BC.scopeLock();
       const int64_t Addend = BC.MIB->getTargetAddend(Add);
       BC.MIB->setOperandToSymbolRef(Adrp, /*OpNum*/ 1, Symbol, Addend,
                                     BC.Ctx.get(), ELF::R_AARCH64_NONE);
     }
   }
 }
 
 void FixRelaxations::runOnFunctions(BinaryContext &BC) {