RFR: 8327701: Remove the xlc toolchain [v2]

[Magnus Ihse Bursie]

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

Also, I believe that the `HOTSPOT_TOOLCHAIN_TYPE=xlc` quirk actually is bad. This means that the clang functionality in `compilerWarnings_gcc.hpp` (where the `_gcc` is hotspot-speak for "clang or gcc") is being ignored, and it means that globalDefinitions_xlc.hpp is in big parts a direct copy of globalDefinitions_gcc.hpp, but apparently lagging in some fixes that has been made in that file.

And it means a lot of lines like this:

#if defined(TARGET_COMPILER_gcc) || defined(TARGET_COMPILER_xlc)


But cleaning up that is left as an exercise to the AIX team; my goal here just primarily to get rid of the old xlc stuff from the build system.

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PR Comment: https://git.openjdk.org/jdk/pull/18172#issuecomment-1985939418