[lworld] RFR: 8377065: [lworld] Fix merge removing VM_Version::supports_fast_class_init_checks() check

[Fei Yang]

Hi,

Please consider this small change fixing a minor issue in latest merge.
The original issue is: https://bugs.openjdk.org/browse/JDK-8370112.
After the latest merge, there is still one runtime check for `VM_Version::supports_fast_class_init_checks()` left in x86 and aarch64 platform specific code.
We should replace them with asserts for consistency with other places. Verified by running `hotspot_valhalla` and `jdk_valhalla` on these two platforms.

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Commit messages:
 - 8377065: [lworld] Fix merge removing VM_Version::supports_fast_class_init_checks() check

Changes: https://git.openjdk.org/valhalla/pull/2020/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=2020&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8377065
  Stats: 4 lines in 2 files changed: 2 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/valhalla/pull/2020.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/2020/head:pull/2020

PR: https://git.openjdk.org/valhalla/pull/2020