Fix detection of ARMv7 and ARM64 CPU features on FreeBSD

[allanjude]

OpenSSL assumes AT_HWCAP = 16 (as on Linux), but on FreeBSD AT_HWCAP = 25

OpenSSL calls elf_auxv_info() with AT_CANARY which returns ENOENT
resulting in all ARM acceleration features being disabled.

CLA: trivial

Checklist

[allanjude]

Would it be preferable to instead do something like:

#ifndef AT_HWCAP
#  define AT_HWCAP 16
#endif

And then use AT_HWCAP to avoid the FreeBSD specific ifdefs?

[t8m]

Would it be preferable to instead do something like:

#ifndef AT_HWCAP
#  define AT_HWCAP 16
#endif

And then use AT_HWCAP to avoid the FreeBSD specific ifdefs?

Yeah, that would look better to me.

[allanjude]

I've opened a different pull request for the alternative version, I agree it is cleaner: #17082

[t8m]

Closing in favor of #17082