RFR: 8327701: Remove the xlc toolchain

Fri Mar 8 15:37:00 UTC 2024

As of [JDK-8325880](https://bugs.openjdk.org/browse/JDK-8325880), building the JDK requires version 17 of IBM Open XL C/C++ (xlc). This is in effect clang by another name, and it uses the clang toolchain in the JDK build. Thus the old xlc toolchain is no longer supported, and should be removed.

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Commit messages:
 - 8327701: Remove the xlc toolchain

Changes: https://git.openjdk.org/jdk/pull/18172/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18172&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8327701
  Stats: 333 lines in 19 files changed: 25 ins; 267 del; 41 mod
  Patch: https://git.openjdk.org/jdk/pull/18172.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18172/head:pull/18172

PR: https://git.openjdk.org/jdk/pull/18172