Revert r330897:

This was intended to be a non-functional change. It wasn't. The commit
message was thus wrong. In addition it broke arm, and merged crypto
related code.

Revert with prejudice.

This revert skips files touched in r316370 since that commit was since
MFCed. This revert also skips files that require $FreeBSD$ property
changes.

Thank you to those who helped me get out of this mess including but not
limited to gonzo, kevans, rgrimes.

Requested by: gjb (re)

Partial merge of the SPDX changes

These changes are incomplete but are making it difficult
to determine what other changes can/should be merged.

No objections from: pfg

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

- Fix style(9) a bit
-- Fix whitespace
-- Use err/errx
-- Remove superfluous braces
- Be a bit more defensive with input from the end-user
- Don't throw a floating point exception by dividing by 0 when processing a
zero-byte file

MFC after: 1 week

Include stdint.h when use intmax_t.

Reported by: bde

Replace PRId64 with "jd" in a printf call. Cast the corresponding value to
intmax_t, because the original type is off_t.

Reported by: bde

Use PRId64 instead of %gd to print an int64_t.

Add the ability to do all read, all write, or random read/write.

Include a very basic (and beta) tool for stressing disks using the POSIX
AIO calls.

This small program queues up a controllable number of concurrent AIO
read operations w/ controllable io size against a disk or regular file.
There are a few other things to add (notably optional write support!)
but it works well enough at the present time to stress the AIO code out
relatively harshly in the disk IO case.