RFR: Store cpu features in AOTCodeCache header [v2]

[Ashutosh Mehra]

> 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.

Ashutosh Mehra has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Merge branch 'premain' into aot-cache-feature-flags
 - Address review comments
   
   Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>
 - Store cpu features in AOTCodeCache header
   
   Signed-off-by: Ashutosh Mehra <asmehra at redhat.com>

-------------

Changes:
  - all: https://git.openjdk.org/leyden/pull/84/files
  - new: https://git.openjdk.org/leyden/pull/84/files/f1dd898f..9b77b82d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=leyden&pr=84&range=01
 - incr: https://webrevs.openjdk.org/?repo=leyden&pr=84&range=00-01

  Stats: 1327 lines in 46 files changed: 211 ins; 847 del; 269 mod
  Patch: https://git.openjdk.org/leyden/pull/84.diff
  Fetch: git fetch https://git.openjdk.org/leyden.git pull/84/head:pull/84

PR: https://git.openjdk.org/leyden/pull/84