[llvm] [PAC][ELF] Place AUTH constants in .data.rel.ro for position dependent code (PR #150418)

[Anatoly Trosinenko via llvm-commits]

================
@@ -333,9 +348,10 @@ SectionKind TargetLoweringObjectFile::getKindForGlobal(const GlobalObject *GO,
       // mergable section, because the linker doesn't take relocations into
       // consideration when it tries to merge entries in the section.
       Reloc::Model ReloModel = TM.getRelocationModel();
-      if (ReloModel == Reloc::Static || ReloModel == Reloc::ROPI ||
-          ReloModel == Reloc::RWPI || ReloModel == Reloc::ROPI_RWPI ||
-          !C->needsDynamicRelocation())
+      if ((ReloModel == Reloc::Static || ReloModel == Reloc::ROPI ||
+           ReloModel == Reloc::RWPI || ReloModel == Reloc::ROPI_RWPI ||
+           !C->needsDynamicRelocation()) &&
+          !containsConstantPtrAuth(C))
         return SectionKind::getReadOnly();
----------------
atrosinenko wrote:

[nit] Maybe it would be more readable to organize the checks along the lines
```cpp
// ...
  } else {
    // First of all, the dynamic linker always needs to fix PtrAuth relocations up.
    if (containsPtrAuth(C))
      return SectionKind::getReadOnlyWithRel();

    // In static, ROPI and RWPI relocation models, the linker will resolve
    // ...
    if (ReloModel == ...)
      return SectionKind::getReadOnly();

    // Otherwise, the dynamic linker needs to fix it up, put it in the
    // writable data.rel section.
    return SectionKind::getReadOnlyWithRel();
```

https://github.com/llvm/llvm-project/pull/150418