* Fix check for newer versions of ICU
The previous test would always trigger, even if the version of ICU
installed didn't require C++17. This was because it incorrectly used
the `test` program, which broke the build on systems without a C++17
compiler.
Tested with macOS 14 and i 7.2.
* Fix broken ICU version check for definition
Same as the previous fix for C++17.
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Co-authored-by: Peter Kokot <peterkokot@gmail.com>
4e21a26db2