RFR: 8305227: [s390x] build broken after JDK-8231349

[Amit Kumar]

This PR moves nmethod entry barrier  from `generate_compiler_stubs()` to `generate_final_stubs()`. Test build for fastdebug, slow debug, release and optimised. Tier1 test in fastdebug seems clean as well.

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Commit messages:
 - moves _nmethod_entry_barrier

Changes: https://git.openjdk.org/jdk/pull/13259/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13259&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8305227
  Stats: 13 lines in 1 file changed: 7 ins; 6 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/13259.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13259/head:pull/13259

PR: https://git.openjdk.org/jdk/pull/13259