RFR: 8338694: x86_64 intrinsic for tanh using libm

[Srinivas Vamsi Parasa]

The goal of this PR is to implement an x86_64 intrinsic for java.lang.Math.tanh() using libm

Benchmark (ops/ms) | Stock JDK | Tanh intrinsic | Speedup
-- | -- | -- | --
MathBench.tanhDouble | 70900 | 95618 | 1.35x

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Commit messages:
 - Fix bug in NaN path
 - 8338694: x86_64 intrinsic for tanh using libm

Changes: https://git.openjdk.org/jdk/pull/20657/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20657&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338694
  Stats: 565 lines in 25 files changed: 556 ins; 0 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/20657.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20657/head:pull/20657

PR: https://git.openjdk.org/jdk/pull/20657