[clang] [clang][Obj-C][PAC] Add support for authenticating block metadata (PR #152978)

[John McCall via cfe-commits]

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@@ -4540,6 +4540,7 @@ defm aarch64_jump_table_hardening: OptInCC1FFlag<"aarch64-jump-table-hardening",
 defm ptrauth_objc_isa : OptInCC1FFlag<"ptrauth-objc-isa", "Enable signing and authentication of Objective-C object's 'isa' field">;
 defm ptrauth_objc_interface_sel : OptInCC1FFlag<"ptrauth-objc-interface-sel", "Enable signing and authentication of Objective-C object's 'SEL' fields">;
 defm ptrauth_objc_class_ro : OptInCC1FFlag<"ptrauth-objc-class-ro", "Enable signing and authentication for ObjC class_ro pointers">;
+defm ptrauth_block_descriptor_pointers : OptInCC1FFlag<"ptrauth-block-descriptor-pointers", "Enable signing and authentication of block descriptors">;
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rjmccall wrote:

Do we really need this option? I know we went through a whole staged adoption for this at Apple, but it seems like something that probably just shouldn't be independently controlled.

https://github.com/llvm/llvm-project/pull/152978