Most C standard library functions are undefined if passed NULL, even
when the corresponding length is zero. This gives them (and, in turn,
all functions which call them) surprising behavior on empty arrays.
Some compilers will miscompile code due to this rule. See also
https://www.imperialviolet.org/2016/06/26/nonnull.html

Add OPENSSL_memcpy, etc., wrappers which avoid this problem.

BUG=23

Change-Id: I95f42b23e92945af0e681264fffaf578e7f8465e
Reviewed-on: https://boringssl-review.googlesource.com/12928
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>

It seems OS X actually cares about symbol resolution and dependencies
when you create a dylib. Probably because they do two-level name
resolution.

(Obligatory disclaimer: BoringSSL does not have a stable ABI and is thus
not suitable for a traditional system-wide library.)

BUG=539603

Change-Id: Ic26c4ad23840fe6c1f4825c44671e74dd2e33870
Reviewed-on: https://boringssl-review.googlesource.com/6131
Reviewed-by: Adam Langley <alangley@gmail.com>

Change-Id: I7ab7ea3cdabc697b2945a50c8d8f349d6b408848
Reviewed-on: https://boringssl-review.googlesource.com/5211
Reviewed-by: Adam Langley <agl@google.com>