[PAuth] Normalize usage of defines

[asl]

__arm64__ define is Apple-specific, however its usage might be misleading. It would make sense to normalize defines usage:

• Explicitly use __arm64e__ define for apple-specific cases
• Use __aarch64__ for common ones

We need to check all usages of __arm64__ / __arm64e__ to ensure proper functionality

[kovdan01]

No changes except the change already introduced in libcxx e8ecdfc3d411e5c3e4207f70f94972083e636cbf are required.

• Despite the fact that __aarch64__ isn't subtarget-specific (and is defined on Apple targets together with __arm64__), there are many places where constructions like the following are used:

  #if defined(__arm64__) || defined(__aarch64__)

  So, it looks like it's a pattern to use them together. Maybe in past __aarch64__ was not defined for Apple's targets and we still have additional check against __arm64__ for compatibility reasons instead of a single check against __aarch64__, maybe there are other historical reasons for such a pattern. Anyway, I consider we can keep it in libcxx as well instead of relying on just __aarch64__ - this is unneeded verbosity, but it keeps things uniform.

• Actually, the already fixed __arm64__ usage in libcxx was the only place where both following conditions are true:

  • it's not Apple-specific code;
  • it's used without the same check against __aarch64__.

  So, there are no non-Apple-specific places where only __arm64__ is checked and which should be fixed by checking __aarch64__ as well.

• __arm64e__ is only used in Apple-specific code except one place: compiler-rt/lib/sanitizer_common/sanitizer_symbolizer_libcdep.cpp. There, we define --default-arch argument for llvm-symbolizer depending on defined macros. We should probably check the llvm-symbolizer behavior for such a case.

[asl]

But maybe we can use __has_feature check here? So, the attribute will be enabled only when pauth ABI is in use?

[kovdan01]

Thanks @asl, I've added a check against __has_feature(ptrauth_calls) here 52420441eaa2ceafa9b7a4d205179f9d21d1b00f: vtable signing is unconditionally enabled when ptrauth-calls are enabled, the only thing that a user can change is whether type/address discrimination are enabled. I've also checked if other places with clang::ptrauth* attributes need to be changed - fortunately, there are no such places.