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

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

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.

Synchronize with laster version of m4 from OpenBSD and NetBSD
This bring better compatibility with gnum4

Reviewed by: cognet
Approved by: cognet
Obtained from: OpenBSD, NetBSD

Mark global functions and/or variables in m4(1) static where possible.

This allows compilers and static analyzers to more thorough analysis.

Fix typos - remove duplicate "the".

PR: bin/154928
Submitted by: Eitan Adler <lists at eitanadler.com>
MFC after: 3 days

Use NULL instead of 0 for the return value of fopen().

Approved by: re (kensmith)

Don't depend on NULL's expansion being a pointer, cast it before it is passed
to variadic functions.

Approved by: das (mentor)

Kill extraneous whitespace.

Functions declared as <type> <identifier>(<nil>) should be declared as
<type> <identifier>(<void-type>) in ANSI C.

Merge local changes again, against ANSIfied m4(1).

Use %zu to print a size_t, not %u and definitely not %d.

Remove WARNS?=2, as GCC will usually throw a fit right now, and I'm not going
to mix WARNS and NO_WERROR.

Submitted by: fenner

Print a size_t as %u not %d.

Pointed out by: mike, des's tinderbox

Crank WARNS.

Cast sizeof() to (int), as it's being compared against an int, not a size_t.
If i is changed to a size_t, it means the logic must be slightly changed later
in the flow, where --i is checked to be >= 0. I am not sure I want to make a
logic change to account for clearing up a warning, when an aesthetic one will
keep from modifying the logic.

Other harmless casts, that I think I've made in the right directions.

Make gpbc() an inline function, rather than an obfuscated macro, make its
scratch space local, rather than global. The previous macro used a dirty
hack (logical AND in place of a conditional) which would lead GCC to throw
a fit (rightly so) as the logical check, as well as the incrementation of
a variable, were not used for anything.

const'ify a few places where gcc3 yells. xstrdup() some global consts in
places where we xstrdup() when not using consts, but tried to assign them
to non-consts before.

Don't use execv(2) if we don't have the kind of arguments it wants.

Reviewed by: asmodai obrien tjr
Submitted by: tjr (a gcc3 build log)

Add __FBSDID, this file was unmodified so it was missed in the initial sweep.

This commit was generated by cvs2svn to compensate for changes in r90744,
which included commits to RCS files with non-trunk default branches.

Import OpenBSD m4 as of today.