check-tcg multi-threaded tests fail on ppc64 on clang-user CI job

clang-user fail example https://gitlab.com/npiggin/qemu/-/jobs/7427207604

The multi-threaded ppc64 tcg tests hit this assertion in glibc, which seems like it must be corruption.

TEST signals on ppc64 signals: allocatestack.c:223: allocate_stack: Assertion `powerof2 (pagesize_m1 + 1)' failed. qemu: uncaught target signal 6 (Aborted) - core dumped

gcc compiled test cases do not fail, and I have not been able to reproduce with clang compile on my local system so far.