When __APPLE__ is defined and HCRYPTO_DEF_PROVIDER is not defined,
define HCRYPTO_DEF_PROVIDER to be "cc" so that Apple's CommonCrypto
implementations are used instead of the built-in "hcrypto"
implementations.
Change-Id: I393e5fc3f6c3b9339c96db58d926ff8ea1867cbb