Makefile: document default SHA-1 backend on OSX
Since [1] the default SHA-1 backend on OSX has been
APPLE_COMMON_CRYPTO. Per [2] we'll skip using it on anything older
than Mac OS X 10.4 "Tiger"[3].
When "DC_SHA1" was made the default in [4] this interaction between it
and APPLE_COMMON_CRYPTO seems to have been missed in. Ever since
DC_SHA1 was "made the default" we've still used Apple's CommonCrypto
instead of sha1collisiondetection on modern versions of Darwin and
OSX.
1.
61067954ce1 (cache.h: eliminate SHA-1 deprecation warnings on Mac
OS X, 2013-05-19)
2.
9c7a0beee09 (config.mak.uname: set NO_APPLE_COMMON_CRYPTO on older
systems, 2014-08-15)
3. We could probably drop "NO_APPLE_COMMON_CRYPTO", as nobody's likely
to care about such on old version of OSX anymore. But let's leave that
for now.
4.
e6b07da2780 (Makefile: make DC_SHA1 the default, 2017-03-17)
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>