testSystemTools: apply root-check on AIX
The TestFileAccess test fails on AIX with this message:
TestFileAccess incorrectly indicated that this is a writable file
If the test is run as root, skip that part of the test as we do on Linux and BSDs. Extend the fix from !173 (merged) and !220 (merged) to AIX hosts too.
Issue: cmake/cmake#23157 (closed)
Edited by Brad King