CI test-build-unified-tree-check-flang on ppc64le-flang-rhel-test fails

[kikairoya]

I noticed some build failures, but they appear to be unrelated to my change:
#143130 (comment)
#143133 (comment)

These failures seem to have first occurred in https://lab.llvm.org/buildbot/#/builders/157/builds/30523, introduced by #143603, although that change also looks unrelated.

[kkwli]

The test no longer fails in the ppc64le-flang-rhel-clang buildbot.