Use getauxval on Android with API level > 18

Use getauxval on Android with API level > 18

We received analytics that devices of the device family Oppo A37x
are crashing with SIGILL when trying to load libcrypto.so.
These crashes were fixed by using the system-supplied getauxval function.

Reviewed-by: Kurt Roeckx <kurt@roeckx.be>
Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/11257)