[llvm] [llvm][AArch64] Autoupgrade function attributes from Module attributes. (PR #82763)

[via llvm-commits]

partaror wrote:

The original pull-request description states:

```
sign-return-address and similar module attributes should be propagated to
the function level before got merged because module flags may contradict and
this information is not recoverable.
```

In this patch, why are we adding attributes to the function which are neither present in the function and nor the module? Currently ,we are adding function attribute with value `false`, if an attribute is neither present in the function and nor the module. This behavior does not conform to the PR description -- attributes which were never present are being propagated. This behavior seems incorrect because default value for the missing attributes might be 'true' in some cases.

https://github.com/llvm/llvm-project/pull/82763