RFR: 8327701: Remove the xlc toolchain [v4]

[Magnus Ihse Bursie]

> 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.

Magnus Ihse Bursie has updated the pull request incrementally with two additional commits since the last revision:

 - Replace CC_VERSION_OUTPUT with CC_VERSION_STRING
 - We need CC_VERSION_OUTPUT before we can check it

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Changes:
  - all: https://git.openjdk.org/jdk/pull/18172/files
  - new: https://git.openjdk.org/jdk/pull/18172/files/e7949499..577715b3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18172&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18172&range=02-03

  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 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