[AArch64] Add native CPU detection for Microsoft Azure Cobalt 100. (#77793)

This patch extends the -mcpu/mtune=native support to handle the
Microsoft Azure Cobalt 100 CPU as a Neoverse N2. We expect users to use
-mcpu=neoverse-n2 when targeting this CPU and all the architecture and
codegen decisions to be identical.

The only difference is that the Microsoft Azure Cobalt 100 has a
different Implementer ID in the /proc/cpuinfo entry that needs to be
detected in getHostCPUNameForARM appropriately.