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

Make sure the first argument to the user function is 16-byte aligned.

Submitted by: tegge

Use %esi to store next ucp pointer. Mark end of stack by
setting %ebp to zero, this avoids new gdb to dump a weird
backtrace.

Save and restore FPU state properly in ucontext_t's.

Reviewed by: deischen, julian
Approved by: -arch

Include <stdlib.h> to have abort() and exit() declared.

Add getcontext, setcontext, makecontext, and swapcontext. These
functions are defined in SUSv2 and the latest POSIX spec.

Thanks to Bernd Walter <ticso@cicely8.cicely.de> for helping debug my
alpha assembly.

Approved by: -arch