[clang] [llvm] [AArch64] Correctly mark Neoverse N2 as an Armv9.0a core (PR #75055)

[David Spickett via llvm-commits]

================
@@ -94,6 +94,11 @@ Changes to the AArch64 Backend
 
 * Added support for Cortex-A520, Cortex-A720 and Cortex-X4 CPUs.
 
+* Neoverse-N2 was incorrectly marked as an Armv8.5a core. This has been
+  changed to an Armv9.0a core. However, crypto options are not enabled
+  by default for Armv9 cores, so `-mcpu=neoverse-n2+crypto` is required
----------------
DavidSpickett wrote:

That is a problem worth fixing but it's not unique to this change unfortunately. Examples like this succeed:
```
$ ./bin/clang -march=armv8.1-a+sve2 /tmp/test.c
```
Which is a larger issue with clang.

At least with this change, `-mcpu=neoverse-n2+sve+sve2` follows the architecture rules where previously it did not. So that's a good improvement.

https://github.com/llvm/llvm-project/pull/75055