RFR: Store cpu features in AOTCodeCache header

[Jan Kratochvil]

On Fri, 4 Jul 2025 20:30:45 GMT, Ashutosh Mehra <asmehra at openjdk.org> wrote:

> This is the initial version of storing cpu features in the AOTCodeCache to verify runtime env has the same cpu capabilities as the assembly env. It covers both x86 and aarch64.
> AOTCodeCache header is updated to store the cpu features in arch-dependent form (although its same for currently supported architectures - x86 and aarch64).
> 
> It also fixes a bug - the `polling_page_vectors_safepoint_handler_blob` can be null if AVX is not present on a system. This causes crash as this blob's entry point is stored in the address table.
> I came across this when I did the assembly run with -XX:UseAVX=0 option.

It can be a future extension but Leyden may also find useful an equivalent of `-XX:CPUFeatures=generic` so that you can store the data on any machine and restore it also on any machine - limiting the CPU feature set in all runs to some reasonable minimum.

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PR Comment: https://git.openjdk.org/leyden/pull/84#issuecomment-3046129476