MFC r281800 (pfg):

patch(1): small include changes.

Mostly to match OpenBSD, no functional change.

MFC r286601 + 286617:

use posix_spawn(3) instead of fork() and exec() manually as suggested
by jmg@.

MFC r276218:

patch: Bring in xstrdup and use it when appropriate.

The function savestr allows NULL return values during Plan A patching so in
case of out of memory conditions, Plan B can step in. In many cases, NULL
value is not properly handled, so use xstrdup here (it's outside Plan A/B
patching, which means that even Plan B relies on successful operations).

Clean up some whitespaces while here

Obtained from: OpenBSD

MFC r276472:

Minor fixes to exit status.

Exit with EXIT_FAILURE for invalid arguments.
Fixes NetBSD-PR 43517.

Print version string to stdout instead of stderr;
it is user-requested and not an error.

Obtained from: NetBSD

MFC r281800 (pfg):

patch(1): small include changes.

Mostly to match OpenBSD, no functional change.

MFC r286601 + 286617:

use posix_spawn(3) instead of fork() and exec() manually as suggested
by jmg@.

MFC r276218:

patch: Bring in xstrdup and use it when appropriate.

The function savestr allows NULL return values during Plan A patching so in
case of out of memory conditions, Plan B can step in. In many cases, NULL
value is not properly handled, so use xstrdup here (it's outside Plan A/B
patching, which means that even Plan B relies on successful operations).

Clean up some whitespaces while here

Obtained from: OpenBSD

MFC r276472:

Minor fixes to exit status.

Exit with EXIT_FAILURE for invalid arguments.
Fixes NetBSD-PR 43517.

Print version string to stdout instead of stderr;
it is user-requested and not an error.

Obtained from: NetBSD