HWCAP_* consts for aarch64 were added to libc in this PR and released in v0.2.95
It looks like these constants were imported into cpufeatures in #456 and the libc version was bumped to 0.2.95 accordingly. But then in #732 libc version was bumped down. I think the minimum libc version should be bumped back up to 0.2.95 to include these constants