[CodeGenPrepare] Fix modification status bug

[aidengrossman]

Summary

This was exposed in https://reviews.llvm.org/D158250 in
CodeGen/X86/statepoint-stack-usage.ll. There was no update to the
modification status in this section.

Co-Authored-By: nikic

[aidengrossman]

Fixes https://github.com/llvm/llvm-project/issues/64938.

[nikic]

LG

llvm/lib/CodeGen/CodeGenPrepare.cpp

simplifyRelocatesOffABase(GCRelocateInst *RelocatedBase,
   // basic block as relocation of base. Relocations from other basic block will
   // be skipped by optimization and we do not care about them.
   for (auto R = RelocatedBase->getParent()->getFirstInsertionPt();
        &*R != RelocatedBase; ++R)
     if (auto *RI = dyn_cast<GCRelocateInst>(R))
       if (RI->getStatepoint() == RelocatedBase->getStatepoint())
         if (RI->getBasePtrIndex() == RelocatedBase->getBasePtrIndex()) {
           RelocatedBase->moveBefore(RI);
+          MadeChange = true;
           break;
         }
 
   for (GCRelocateInst *ToReplace : Targets) {
     assert(ToReplace->getBasePtrIndex() == RelocatedBase->getBasePtrIndex() &&
            "Not relocating a derived object of the original base object");
     if (ToReplace->getBasePtrIndex() == ToReplace->getDerivedPtrIndex()) {
       // A duplicate relocate call. TODO: coalesce duplicates.