[clang] [llvm] [MC,llvm-readobj,yaml2obj] Support CREL relocation format (PR #91280)

[Fangrui Song via cfe-commits]

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@@ -474,9 +480,28 @@ struct Elf_Rel_Impl<ELFType<Endianness, true>, true>
     : public Elf_Rel_Impl<ELFType<Endianness, true>, false> {
   LLVM_ELF_IMPORT_TYPES(Endianness, true)
   static const bool IsRela = true;
+  static const bool IsCrel = false;
   Elf_Sxword r_addend; // Compute value for relocatable field by adding this.
 };
 
+template <bool Is64> struct Elf_Crel_Impl {
+  using uint = std::conditional_t<Is64, uint64_t, uint32_t>;
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MaskRay wrote:

Using Is64 instead of ELFType is intentional to avoid unneeded endianness difference. The structure is for in-memory representation and has no endianness difference.

I added a comment before `struct Elf_Crel_Impl`.

https://github.com/llvm/llvm-project/pull/91280