RFR: 8327701: Remove the xlc toolchain [v2]

[Erik Joelsson]

On Fri, 8 Mar 2024 15:48:08 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

>> 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 one additional commit since the last revision:
> 
>   Revert SEARCH_PATH changes

Build changes look good to me, but needs review and verification from the AIX folks.

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Marked as reviewed by erikj (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/18172#pullrequestreview-1925621925