MFC:
r295924: Make sure that hash-based db files fsync befor closing/syncing.
r295925: We no longer need O_SYNC pwd_mkd
r295465: We no longer need O_SYNC on services_mkdb
r295800: We no longer need O_SYNC on cap_mkdb

This should improve the performance of building db files.

MFC r293312:

Make cap_mkdb and services_mkdb file operations sync

Similar fix was done for passwd and group operations in r285050. When a
temporary file is created and then renamed to replace official file there
are no checks to make sure data was written to disk and if a power cycle
happens at this time, system can end up with a 0 length file

Approved by: bapt
Sponsored by: Netgate
Differential Revision: https://reviews.freebsd.org/D2982

MFC 261030:
Similar to cap_mkdb(1), add endianness support to services_mkdb(1)
to support cross-builds once this is invoked during releases.

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

Remove contractions.

Move uniq() prototype into extern.h.

More -Wmissing-variable-declarations fixes.

In addition to adding missing `static' keywords:
- bin/dd: Pull in `extern.h' to guarantee consistency with source file.
- libexec/rpc.rusersd: Move shared globals into an extern.h.
- libexec/talkd: Move `debug' and `hostname' into extern.h.
- usr.bin/cksum: Put counters in extern.h, as they are used by ckdist/mtree.
- usr.bin/m4: Move `end_result' into extern.h.
- usr.sbin/services_mkdb: Move shared globals into an extern.h.

Revise markup, mainly.

Fix compilation error on amd64.

Reported by: stefanf
MFC after: 2 weeks

Fix compilation error on 9-CURRENT.

Reported by: nyan
MFC after: 2 weeks

services_mkdb; generate db file from services(5) to increase
speed of getserv*()

Obtained from: NetBSD
MFC after: 2 weeks