RFR: 8287686: Add assertion to ensure that disarm value offset < 128

[Zhengyu Gu]

Please review this trivial patch to ensure disarm value offset is less than 128.

At least on x86_64, nmethod entry barrier encodes disarmed value offset as disp8 immed, overflowing the value can result crashes, see [JDK-8244420](https://bugs.openjdk.java.net/browse/JDK-8244420) for details.

Test:

- [x] jdk_loom and hotspot_loom on Linux x86_64

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Commit messages:
 - 8287686: Add assertion to ensure that disarm value offset < 128

Changes: https://git.openjdk.java.net/jdk/pull/8977/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8977&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8287686
  Stats: 5 lines in 1 file changed: 4 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8977.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8977/head:pull/8977

PR: https://git.openjdk.java.net/jdk/pull/8977