RFR: 8338694: x86_64 intrinsic for tanh using libm [v3]

[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

Srinivas Vamsi Parasa has updated the pull request incrementally with one additional commit since the last revision:

  update libm tanh reference test with code review suggestions

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/20657/files
  - new: https://git.openjdk.org/jdk/pull/20657/files/4739ad45..39350a37

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20657&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20657&range=01-02

  Stats: 7 lines in 1 file changed: 4 ins; 0 del; 3 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