[devmgr][fs-management][zxcrypt] Add zxcrypt detection

This CL adds zxcrypt volume detection and auto-binding. Long term,
this will only work for zxcrypt volumes using unattended encryption,
that is, those not depending on user authentication.

Change-Id: Iaf97e44ce63b467c7a714df8adccc9adf124e74d

[paver] Add zxcrypt support

This CL adds a flag to FVM sparse containers. This flag
indicates to the disk paver that it should use a zxcrypt volume
on top of the FVM partition. The ability to set the flag in the
host FVM tool will be added in a later CL.

Change-Id: Ica8a416ca7244b1bf8e045ededb2bcfe845092f5

[ulib][zxcpp] Mark all symbols as hidden

Make sure a shared library built with zxcpp doesn't export zxcpp symbols.

Change-Id: I22294fb98752f3c4408faa6bb8b47d48a28786e8

[zxcrypt] enable some integer sanitization

Enable the integer-divide-by-zero (relevant for ARM only) and
signed-integer-overflow checkers. This will add in-code detection for
some classes of undefined integer behavior.

Limit this to zxcrypt for now, as this is just an experiment.

SEC-53: Build a system that is robust against vulnerabilities

Change-Id: I89a5aca790c7325aa5de4d153a1f53036a14c814

[zxcrypt] more moving to compiler intrinsics

See ZX-1747

Change-Id: Idae93cf343fb42560fe83b6faa4e99f4ae35edb8

[block][zxcrypt] remove support for iotxns

Change-Id: If4f703facbfa9d58e85f45283123a3d8af4d27ec

[crypto][fdio][zxcrypt] Improve debug output

This CL improves fdio/debug's xprintf with location info.

Change-Id: Idd05c0439258ed3fe160086bcce05575eddbc38b

[zxcrypt] Rename superblock to volume

zxcrypt::Superblock evolved beyond just an interface for a single block
of metadata into something more like a zxcrypt volume interface. This
CL renames the class to reflect that.

Change-Id: I8602a9531687df31e84f701e277f07238c519b6e

[zxcrypt] Add Superblock class

This CL adds Superblock, which encapsulates how the cryptographic
metadata is stored and retrieved by zxcrypt. I/O performance is not as
critical a concern here, as the superblock is generally only involved in
'lifecycle' events of a zxcrypt device, that is formatting, binding,
rekeying, and shredding, and not individual data transfers.

Change-Id: I73cebf8d653cee9c00ce7a952bc75852361fec8b