crypto/armcap.c: mask SHA512 hardware detection on iOS.

When running iOS application from command line it's impossible to
get past the failing capability detection. This is because it's
executed under debugger and iOS debugger is impossible to deal with.
[If Apple implements SHA512 in silicon, it would have to be detected
with sysctlbyname.]

Reviewed-by: Rich Salz <rsalz@openssl.org>