Use transfer by reference instead of value to make some space more efficient

[XinWang10]

Summary

Some enumerate function transfer parameter by value and not by reference,
I think these members are big enough, can use reference to reduce the mem
copy.

[skan]

Do not use simple "I think these members are big enough". "auto" is used for type here and the concrete type is not explicit for the reviewers. Please provide more justification.

llvm/include/llvm/Object/ELF.h

 template <class ELFT> void ELFFile<ELFT>::createFakeSections() {
   if (!FakeSections.empty())
     return;
   auto PhdrsOrErr = program_headers();
   if (!PhdrsOrErr)
     return;
 
   FakeSectionStrings += '\0';
-  for (auto [Idx, Phdr] : llvm::enumerate(*PhdrsOrErr)) {
+  for (auto& [Idx, Phdr] : llvm::enumerate(*PhdrsOrErr)) {
     if (Phdr.p_type != ELF::PT_LOAD || !(Phdr.p_flags & ELF::PF_X))
       continue;
     Elf_Shdr FakeShdr = {};
     FakeShdr.sh_type = ELF::SHT_PROGBITS;
     FakeShdr.sh_flags = ELF::SHF_ALLOC | ELF::SHF_EXECINSTR;
     FakeShdr.sh_addr = Phdr.p_vaddr;
     FakeShdr.sh_size = Phdr.p_memsz;
     FakeShdr.sh_offset = Phdr.p_offset;

llvm/lib/CodeGen/MLRegallocEvictAdvisor.cpp

for (const auto *L : Intervals) {
     RW += LIFC.RW;
 
     IndVarUpdates += LIFC.IndVarUpdates;
 
     HintWeights += LIFC.HintWeights;
     NrRematerializable += LIFC.IsRemat;
 
     if (EnableDevelopmentFeatures) {
-      for (auto CurrentSegment : LI) {
+      for (auto &CurrentSegment : LI) {
         LRPosInfo.push_back(
             LRStartEndInfo{CurrentSegment.start, CurrentSegment.end, Pos});
       }
     }
   }
   size_t Size = 0;
   if (!Intervals.empty()) {
     StartBBFreq =