The sysdeps/powerpc/powerpc64/strncmp.S variant crashes due to a page
boundary handling bug. It is not used on ppc64le because the POWER8
variant takes precedence (and on RHEL9, we always use the POWER9
variant). Upstream removed these old variants, so this commit just
backports it. It avoids interfering with further testing.
Resolves: RHEL-60466
