Makefile: add support for Apple CommonCrypto facility
As of Mac OS X 10.7, Apple deprecated all OpenSSL functions due to
OpenSSL ABI instability, thus leading to build warnings. As a
replacement, Apple encourages developers to migrate to its own (stable)
CommonCrypto facility.
Introduce boilerplate which controls whether Apple's CommonCrypto
facility is employed (enabled by default). Also add a
NO_APPLE_COMMON_CRYPTO build flag with which the user can opt out to
use OpenSSL instead.
[es: extracted CommonCrypto-related Makefile boilerplate into separate
introductory patch]
Signed-off-by: David Aguilar <davvid@gmail.com>
Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>