Codegen tests for Arm Cortex-R82
This PR adds checks to the `aarch64v8r-unknown-none` target to verify that if the Cortex-R82 CPU is enabled (with `-Ctarget-cpu=cortex-r82`), that the appropriate additional AArch64 features are enabled.
This is important because Cortex-R82 is (currently) the only processor implementing Armv8-R AArch64 and it implements a number of Armv8 features over and above the baseline for the architecture. Many of these features are of interest to safety-critical firmware development (for example `FEAT_RASv1p1`, which adds support for the *RAS Common Fault Injection Model Extension*) and so we anticipate them being enabled when building such firmware.
We are offering these tests upstream in-lieu of a full Cortex-R82 specific target because we understand the Project has a preference for architecture-baseline targets over CPU-specific targets.
~~This PR builds on and requires https://github.com/rust-lang/rust/pull/150863, but we've pulled them out as a separate PR.~~ That PR has been merged.
## Ownership
This PR was developed by Ferrous Systems on behalf of Arm. Arm is the owner of these changes.
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