[BOLT] Move phdr typedef to cpp file

[urnathan]

Summary

This typedef is only used inside the RewriteInstance source file, let's not
expose it in the header file -- even if private.

This makes it easier to support an ELF32 ABI.

[maksfb]

LGTM. Please add NFC (or NFCI) to the title.

bolt/include/bolt/Rewrite/RewriteInstance.h

public:
   std::optional<std::string> getPrintableBuildID() const;
 
   /// If this instance uses a profile, return appropriate profile reader.
   const ProfileReaderBase *getProfileReader() const {
     return ProfileReader.get();
   }
 
 private:
-  using ELF64LEPhdrTy = object::ELF64LEFile::Elf_Phdr;
-
   /// Populate array of binary functions and other objects of interest
   /// from meta data in the file.
   void discoverFileObjects();
 
   /// Process fragments, locate parent functions.
   void registerFragments();
 
   /// Read info from special sections. E.g. eh_frame and .gcc_except_table

bolt/lib/Rewrite/RewriteInstance.cpp

 #endif
 
   llvm_unreachable("architecture unsupported by MCPlusBuilder");
 }
 
 } // namespace bolt
 } // namespace llvm
 
+using ELF64LEPhdrTy = ELF64LEFile::Elf_Phdr;
+
 namespace {
 
 bool refersToReorderedSection(ErrorOr<BinarySection &> Section) {
   return llvm::any_of(opts::ReorderData, [&](const std::string &SectionName) {
     return Section && Section->getName() == SectionName;
   });
 }