This introduces the attribute discussed in

https://discourse.llvm.org/t/rfc-function-type-attribute-to-prevent-cfi-instrumentation/85458.

The proposed name has been changed from `no_cfi` to
`cfi_unchecked_callee` to help differentiate from `no_sanitize("cfi")`
more easily. The proposed attribute has the following semantics:

1. Indirect calls to a function type with this attribute will not be
instrumented with CFI. That is, the indirect call will not be checked.
Note that this only changes the behavior for indirect calls on pointers
to function types having this attribute. It does not prevent all
indirect function calls for a given type from being checked.
2. All direct references to a function whose type has this attribute
will always reference the true function definition rather than an entry
in the CFI jump table.
3. When a pointer to a function with this attribute is implicitly cast
to a pointer to a function without this attribute, the compiler will
give a warning saying this attribute is discarded. This warning can be
silenced with an explicit C-style cast or C++ static_cast.

Allows the __ptrauth qualifier to be applied to pointer sized integer types,
updates Sema to ensure trivially copyable, etc correctly handle address
discriminated integers, and updates codegen to perform authentication
around arithmetic on the types.

It isn't used and is redundant with the result pointer type argument.
A more reasonable API would only have LangAS parameters, or IR parameters,
not both. Not all values have a meaningful value for this. I'm also
not sure why we have this at all, it's not overridden by any targets and
further simplification is possible.

The qualifier allows programmer to directly control how pointers are
signed when they are stored in a particular variable.

The qualifier takes three arguments: the signing key, a flag specifying
whether address discrimination should be used, and a non-negative
integer that is used for additional discrimination.

```
typedef void (*my_callback)(const void*);
my_callback __ptrauth(ptrauth_key_process_dependent_code, 1, 0xe27a) callback;
```

Co-Authored-By: John McCall rjmccall@apple.com

The test file is over 4GiB, which is too big, so I didn’t submit it.

Make the memory representation of boolean vectors in HLSL, vectors of
i32.
Allow boolean swizzling for boolean vectors in HLSL.
Add tests for boolean vectors and boolean vector swizzling.
Closes #91639

It is an alternative to
https://github.com/llvm/llvm-project/pull/127525.
Close https://github.com/llvm/llvm-project/issues/127475.

Implement HLSL Aggregate Splat casting that handles splatting for arrays
and structs, and vectors if splatting from a vec1.
Closes #100609 and Closes #100619 
Depends on #118842

Implement HLSLElementwiseCast excluding support for splat cases
Do not support casting types that contain bitfields.
Partly closes https://github.com/llvm/llvm-project/issues/100609 and
partly closes https://github.com/llvm/llvm-project/issues/100619
Re-land #118842 after fixing warning as an error, found by a buildbot.