compiler_types: Introduce __nocfi_generic

compiler_types: Introduce __nocfi_generic

There are two different ways that LLVM can expand kCFI operand bundles
in LLVM IR: generically in the middle end or using an architecture
specific sequence when lowering LLVM IR to machine code in the backend.
The generic pass allows any architecture to take advantage of kCFI but
the expansion of these bundles in the middle end can mess with
optimizations that may turn indirect calls into direct calls when the
call target is known at compile time, such as after inlining.

Add __nocfi_generic, dependent on an architecture selecting
CONFIG_ARCH_USES_CFI_GENERIC_LLVM_PASS, to disable kCFI bundle
generation in functions where only the generic kCFI pass may cause
problems.

Link: https://github.com/ClangBuiltLinux/linux/issues/2124
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Link: https://patch.msgid.link/20251025-idpf-fix-arm-kcfi-build-error-v1-1-ec57221153ae@kernel.org
Signed-off-by: Kees Cook <kees@kernel.org>