[jdk21u] RFR: 8315088: C2: assert(wq.size() - before == EMPTY_LOOP_SIZE) failed: expect the EMPTY_LOOP_SIZE nodes of this body if empty

[Aleksey Shipilev]

Clean backport to fix JDK 21 regression. The change was in mainline for 1.5 months, and there is no recorded bugtail.

Additional testing:
 - [x] macos-aarch64-server-fastdebug, new regression test fails without the patch, passes with it
 - [ ] linux-aarch64-server-fastdebug, `tier1 tier2 tier3`

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Commit messages:
 - Backport fe4f90021ffd44cb0af34f39d4ca0a7e44605c92

Changes: https://git.openjdk.org/jdk21u/pull/275/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u&pr=275&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315088
  Stats: 55 lines in 2 files changed: 54 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk21u/pull/275.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u.git pull/275/head:pull/275

PR: https://git.openjdk.org/jdk21u/pull/275