[jdk21u-dev] RFR: 8325672: C2: allocate PhaseIdealLoop::_loop_or_ctrl from C->comp_arena()

[Aleksey Shipilev]

Simple fix to resolve C2 use-after-free bug introduced in JDK 21.

Additional testing:
 - [ ] Linux AArch64 server fastdebug, `tier{1,2,3,4}`

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Commit messages:
 - Backport 74b90aa87e7cfa52ac09bf2e57258d792f740f00

Changes: https://git.openjdk.org/jdk21u-dev/pull/261/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=261&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8325672
  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/261.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/261/head:pull/261

PR: https://git.openjdk.org/jdk21u-dev/pull/261