RFR: JDK-8325264: two compiler/intrinsics/float16 tests fail after JDK-8324724

[Bhavana Kilambi]

Fix for two JTREG test failures on OS_X after this commit - https://github.com/openjdk/jdk/commit/51853f7488afa69c0d14b0e96f1da84822cd83f1.

This is due to no permission to execute the stub code in the code cache. This patch fixes this problem by acquiring "WXExec" to be able to execute the instructions in code cache.

Both the tests - compiler/intrinsics/float16/TestAllFloat16ToFloat.java and compiler/intrinsics/float16/Binary16ConversionNaN.java pass on a MacOS machine.

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Commit messages:
 - JDK-8325264: two compiler/intrinsics/float16 tests fail after JDK-8324724

Changes: https://git.openjdk.org/jdk/pull/17733/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17733&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8325264
  Stats: 7 lines in 2 files changed: 3 ins; 3 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/17733.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17733/head:pull/17733

PR: https://git.openjdk.org/jdk/pull/17733