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>

I screwed up the |EVP_CIPHER| parameters for XTS when I first imported
it, and there were no tests to catch it.  (The problem was that
|EVP_CIPH_XTS_MODE| means “the key size is actually twice what it says
here.”)

With these changes, OpenSSL's tests pass.

(Along the way, make a few other things about XTS slightly less
decrepit.)

Change-Id: Icbfbc5e6d532d1c132392ee366f9cab42802d674
Reviewed-on: https://boringssl-review.googlesource.com/6529
Reviewed-by: Adam Langley <agl@google.com>

gcm_test.cc needs to access the internal GCM symbols. This is
unfortunate because it means that they have to be marked OPENSSL_EXPORT
just for this.

To compensate, modes.h is removed and its contents copied into
crypto/modes/internal.h.

Change-Id: I1777b2ef8afd154c43417137673a28598a7ec30e
Reviewed-on: https://boringssl-review.googlesource.com/6360
Reviewed-by: Adam Langley <alangley@gmail.com>

arm_arch.h is included from ARM asm files, but lives in crypto/, not
openssl/include/. Since the asm files are often built from a different
location than their position in the source tree, relative include paths
are unlikely to work so, rather than having crypto/ be a de-facto,
second global include path, this change moves arm_arch.h to
include/openssl/.

It also removes entries from many include paths because they should be
needed as relative includes are always based on the locations of the
source file.

Change-Id: I638ff43d641ca043a4fc06c0d901b11c6ff73542
Reviewed-on: https://boringssl-review.googlesource.com/5746
Reviewed-by: Adam Langley <agl@google.com>

Change-Id: I63c70f93a0f9395673c9fbe01eb5d864a14a48b6
Reviewed-on: https://boringssl-review.googlesource.com/5520
Reviewed-by: Adam Langley <agl@google.com>
Reviewed-by: Matt Braithwaite <mab@google.com>