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

MFC r313404:

Improve libnetbsd compatibility with NetBSD

This change is being made to diff reduce/reduce duplication in
contrib/netbsd-tests and to facilitate further porting of software from
NetBSD

Add the following headers:
- sys/event.h:
-- sys/types.h is required for kqueue on FreeBSD, but not NetBSD.
- sys/types.h:
-- NBBY is defined in sys/param.h on FreeBSD, not sys/types.h like on NetBSD.
Pull in sys/param.h to have parity with NetBSD.
- sys/wait.h:
-- Define wrusage as __wrusage for parity with NetBSD typedef.
- glob.h
-- Define __gl_stat_t as "struct stat" for parity with NetBSD typedef.
- pthread.h:
-- Pull in pthread_np.h for _np functions defined separately on FreeBSD.

Improve compatibility with NetBSD in the following headers:

- sha1.h:
-- define SHA1_CTX as SHA_CTX
-- define SHA1Final as SHA1_Final
- sha2.h:
-- #include sha384 to pick up all of the SHA 384 bit macros and definitions.
- util.h:
-- Add sys/types.h to util.h to pollute the header for types used in
flags_to_string and string_to_flags (u_long) as NetBSD doesn't require them
for the functions.

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

Add libnetbsd, a thin compatibility layer intended to allow a limited
set of NetBSD software to compile as part of the FreeBSD build with
little or no modifiction. It is built as a static library and not
installed for general use. Likewise, its header files are not
installed.

Sponsored by: DARPA, AFRL