[MISched][scheduleDump] Use stable_sort to prevent test failures.

[fpetrogalli]

Summary

When building the compiler with -DLLVM_ENABLE_EXPENSIVE_CHECKS=ON,
sometimes resources that are dumped in scheduled traces gets reordered
even if they are booked in the same cycle. Using stable_sort
guarantees that such occasional reordering does not happen.

This change should fix failures like the one seen in
https://lab.llvm.org/buildbot/#/builders/16/builds/49592.

[RKSimon]

LGTM - cheers

llvm/lib/CodeGen/MachineScheduler.cpp

for (MachineInstr &MI : *this) {
     dbgs() << "|\n";
     const MCSchedClassDesc *SC = getSchedClass(SU);
 
     SmallVector<MCWriteProcResEntry, 4> ResourcesIt(
         make_range(SchedModel.getWriteProcResBegin(SC),
                    SchedModel.getWriteProcResEnd(SC)));
 
     if (MISchedSortResourcesInTrace)
-      llvm::sort(ResourcesIt.begin(), ResourcesIt.end(),
+      llvm::stable_sort(ResourcesIt,
                         [](const MCWriteProcResEntry &LHS,
                            const MCWriteProcResEntry &RHS) -> bool {
                           return LHS.StartAtCycle < RHS.StartAtCycle ||
                                  (LHS.StartAtCycle == RHS.StartAtCycle &&
                                   LHS.Cycles < RHS.Cycles);
                         });
     for (const MCWriteProcResEntry &PI : ResourcesIt) {
       C = FirstCycle;
       const std::string ResName =
           SchedModel.getResourceName(PI.ProcResourceIdx);
       dbgs() << llvm::right_justify(ResName + " ", HeaderColWidth);
       for (; C < SU->TopReadyCycle + PI.StartAtCycle; ++C) {
         dbgs() << llvm::left_justify("|", ColWidth);
       }
for (MachineInstr &MI : *this) {
     }
     dbgs() << "|\n";
     const MCSchedClassDesc *SC = getSchedClass(SU);
     SmallVector<MCWriteProcResEntry, 4> ResourcesIt(
         make_range(SchedModel.getWriteProcResBegin(SC),
                    SchedModel.getWriteProcResEnd(SC)));
 
     if (MISchedSortResourcesInTrace)
-      llvm::sort(ResourcesIt.begin(), ResourcesIt.end(),
+      llvm::stable_sort(ResourcesIt,
                         [](const MCWriteProcResEntry &LHS,
                            const MCWriteProcResEntry &RHS) -> bool {
                           return LHS.StartAtCycle < RHS.StartAtCycle ||
                                  (LHS.StartAtCycle == RHS.StartAtCycle &&
                                   LHS.Cycles < RHS.Cycles);
                         });
     for (const MCWriteProcResEntry &PI : ResourcesIt) {
       C = FirstCycle;
       const std::string ResName =
           SchedModel.getResourceName(PI.ProcResourceIdx);
       dbgs() << llvm::right_justify(ResName + " ", HeaderColWidth);
       for (; C > ((int)SU->BotReadyCycle - (int)PI.StartAtCycle); --C) {
         dbgs() << llvm::left_justify("|", ColWidth);
       }