crypto/mem.c: bump alignment to sizeof(void *) when posix_memaling() is used

crypto/mem.c: bump alignment to sizeof(void *) when posix_memaling() is used

Per [1]:

    The value of alignment shall be a power of two multiple of sizeof(void *).

[1] https://pubs.opengroup.org/onlinepubs/9799919799/functions/posix_memalign.html

Signed-off-by: Eugene Syromiatnikov <esyr@openssl.org>
Reviewed-by: Saša Nedvědický <sashan@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Paul Dale <ppzgs1@gmail.com>
Reviewed-by: Neil Horman <nhorman@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/28059)