[BOLT] Fix data reoder for aarch64

[yota9]

Summary

Use proper relocation for aarch64

[rafauler]

Be aware that data reorder is experimental and haven't been tested in a while.

[yota9]

@rafaelauler Yes, I know about that. I don't really use it (although I think we can give it a try), but it seems to be working fine, the test in the RW segment patch shows it :)

bolt/include/bolt/Core/Relocation.h

struct Relocation {
   static uint64_t getNone();
 
   /// Return code for a PC-relative 4-byte relocation
   static uint64_t getPC32();
 
   /// Return code for a PC-relative 8-byte relocation
   static uint64_t getPC64();
 
+  /// Return code for a ABS 8-byte relocation
+  static uint64_t getAbs64();
+
   /// Return true if this relocation is PC-relative. Return false otherwise.
   bool isPCRelative() const { return isPCRelative(Type); }
 
   /// Return true if this relocation is R_*_RELATIVE type. Return false
   /// otherwise.
   bool isRelative() const { return isRelative(Type); }
 
   /// Emit relocation at a current \p Streamer' position. The caller is

bolt/lib/Core/BinarySection.cpp

LLVM_DEBUG(dbgs() << "BOLT-DEBUG: " << BD->getName() << " @ " << OS.tell()
                       << "\n");
     OS.write(&Src[SrcOffset], BD->getOutputSize());
   }
   if (Relocations.empty()) {
     // If there are no existing relocations, tack a phony one at the end
     // of the reordered segment to force LLVM to recognize and map this
     // section.
     MCSymbol *ZeroSym = BC.registerNameAtAddress("Zero", 0, 0, 0);
-    addRelocation(OS.tell(), ZeroSym, ELF::R_X86_64_64, 0xdeadbeef);
+    addRelocation(OS.tell(), ZeroSym, Relocation::getAbs64(), 0xdeadbeef);
 
     uint64_t Zero = 0;
     OS.write(reinterpret_cast<const char *>(&Zero), sizeof(Zero));
   }
   auto *NewData = reinterpret_cast<char *>(copyByteArray(OS.str()));
   Contents = OutputContents = StringRef(NewData, OS.str().size());
   OutputSize = Contents.size();
 }

bolt/lib/Core/Relocation.cpp

 }
 
 bool Relocation::isPCRelative(uint64_t Type) {
   if (Arch == Triple::aarch64)
     return isPCRelativeAArch64(Type);
   return isPCRelativeX86(Type);
 }
 
+uint64_t Relocation::getAbs64() {
+  if (Arch == Triple::aarch64)
+    return ELF::R_AARCH64_ABS64;
+  return ELF::R_X86_64_64;
+}
+
 size_t Relocation::emit(MCStreamer *Streamer) const {
   const size_t Size = getSizeForType(Type);
   MCContext &Ctx = Streamer->getContext();
   if (isPCRelative(Type)) {
     MCSymbol *TempLabel = Ctx.createNamedTempSymbol();
     Streamer->emitLabel(TempLabel);
     const MCExpr *Value = nullptr;
     if (Symbol) {