RFR: 8317575: AArch64: C2_MacroAssembler::fast_lock uses rscratch1 for cmpxchg result

[Stefan Karlsson]

Please review this removal a potentially problematic usage of rscratch1 in C2_MacroAssembler::fast_lock.

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Commit messages:
 - 8317575: AArch64: C2_MacroAssembler::fast_lock uses rscratch1 for cmpxchg result

Changes: https://git.openjdk.org/jdk/pull/16049/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16049&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317575
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/16049.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16049/head:pull/16049

PR: https://git.openjdk.org/jdk/pull/16049