RFR: 8350663: AArch64: Enable UseSignumIntrinsic by default

[Patrick Zhang]

According to tests on Arm CPUs Neoverse-N1/N2/V1/V2 and Ampere-Altra/AmpereOne, `-XX:+UseSignumIntrinsic` can provide consistent positive performance boost on singnum microbenchmarks (1-4,5,7 in below list) and no obvious regression (ops/s change <0.1%) on other relevant tests (6,9-12). In addition, "_Apple M1 shows no regression with signum intrinsics_" (verified by @theRealAph). So, it can be the time to enable this UseSignumIntrinsic flag by default for aarch64-port. By the way, x86 and riscv ports have already configured it on by default. 

Tests: passed JTReg tier1 tests on Ampere-1A, no regression found, and particularly checked test results of two signum cases (13,14), both are in good state.


1. org.openjdk.bench.java.lang.MathBench.signumDouble
2. org.openjdk.bench.java.lang.MathBench.signumFloat
3. org.openjdk.bench.java.lang.StrictMathBench.sigNumDouble
4. org.openjdk.bench.java.lang.StrictMathBench.signumFloat
5. org.openjdk.bench.vm.compiler.Signum._1_signumFloatTest
6. org.openjdk.bench.vm.compiler.Signum._2_overheadFloat
7. org.openjdk.bench.vm.compiler.Signum._3_signumDoubleTest
8. org.openjdk.bench.vm.compiler.Signum._4_overheadDouble
9. org.openjdk.bench.vm.compiler.Signum._5_copySignFloatTest
10. org.openjdk.bench.vm.compiler.Signum._6_overheadCopySignFloat
11. org.openjdk.bench.vm.compiler.Signum._7_copySignDoubleTest
12. org.openjdk.bench.vm.compiler.Signum._8_overheadCopySignDouble
13. JTReg: compiler/vectorization/TestSignumVector.java
14. JTReg: compiler/intrinsics/math/TestSignumIntrinsic.java

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Commit messages:
 - 8350663: AArch64: Enable UseSignumIntrinsic by default

Changes: https://git.openjdk.org/jdk/pull/23893/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23893&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8350663
  Stats: 4 lines in 1 file changed: 0 ins; 3 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/23893.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23893/head:pull/23893

PR: https://git.openjdk.org/jdk/pull/23893