[libcxx][AArch64][PAC] Fix std::type_info vtable discrimination

For non-Darwin targets, the vtable discrimination for `std::type_info`
was not correct since `__arm64__` macro is defined only for Darwin.
Use `__aarch64__` to fix ifdef for non-Darwin.

Author: kovdan01

libcxx/include/typeinfo

@@ -299,7 +299,9 @@ struct __type_info_implementations {
      __impl;
 };
 
-#if defined(__arm64__) && __has_cpp_attribute(clang::ptrauth_vtable_pointer)
+#if (defined(__arm64__) || defined(__aarch64__)) && \
+    __has_feature(ptrauth_calls) && \
+    __has_cpp_attribute(clang::ptrauth_vtable_pointer)
 #define _LIBCPP_TYPE_INFO_VTABLE_POINTER_AUTH \
    [[clang::ptrauth_vtable_pointer(process_independent, no_address_discrimination, no_extra_discrimination)]]
 #else