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

libc: Use namespace.h in a few more files.

libc now no longer calls fstat(), socketpair() and wait(), only the
underscore-prefixed versions (_waitpid() instead of wait()).

- ANSIfy
- Remove the redundant _PATH_RSH definition (paths.h at r96194);
- Use pid_t for PIDs
- Note that we are at the same level of OpenBSD's counterpart of
revision 1.7 (r94757).

No functional changes.

MFC after: 2 weeks

Eliminate 19 warnings in libc (at level WARNS=2) of the
`implicit declaration of function' variety.

Add awareness of an IPv6.

MFC after: 1 week

Quoting log message for OpenBSD rev 1.7:
``Tack on MagniComp (BSD) license since this originally came from rdist.''

Obtained from: OpenBSD

- Put missing prototype for rcmd() in <unistd.h>.
- Clean up the manpage.
- style(9) rcmdsh.c.

Committed from: BSDCon/EU 2k+1 terminal room

Allow users to specify a command to use as remote command instead of
using rcmd directly. This has been in my tree for a long time, but we
may need to sync with OpenBSD before MFC.

Obtained from: openbsd
PR: 15830

MFC after: 2 months