MFC r290492:
Move intmax_t and uintmax_t type declarations to sys/_stdint.h.

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

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

Make the wchar_t type machine dependent.

This is required for ARM EABI. Section 7.1.1 of the Procedure Call for the
ARM Architecture (AAPCS) defines wchar_t as either an unsigned int or an
unsigned short with the former preferred.

Because of this requirement we need to move the definition of __wchar_t to
a machine dependent header. It also cleans up the macros defining the limits
of wchar_t by defining __WCHAR_MIN and __WCHAR_MAX in the same machine
dependent header then using them to define WCHAR_MIN and WCHAR_MAX
respectively.

Discussed with: bde

Add a pointless and superfluous GNUism that people at a certain large data
aggregation and advertising company seem to believe is standard.

Approved by: dim (mentor)

Don't duplicate define the stdint types.

o Merge <machine/ansi.h> and <machine/types.h> into a new header
called <machine/_types.h>.
o <machine/ansi.h> will continue to live so it can define MD clock
macros, which are only MD because of gratuitous differences between
architectures.
o Change all headers to make use of this. This mainly involves
changing:
#ifdef _BSD_FOO_T_
typedef _BSD_FOO_T_ foo_t;
#undef _BSD_FOO_T_
#endif
to:
#ifndef _FOO_T_DECLARED
typedef __foo_t foo_t;
#define _FOO_T_DECLARED
#endif

Concept by: bde
Reviewed by: jake, obrien

Create a new header <machine/_stdint.h> for storing MD parts of
<stdint.h>. Previously, parts were defined in <machine/ansi.h> and
<machine/limits.h>. This resulted in two problems:
(1) Defining macros in <machine/ansi.h> gets in the way of that
header only defining types.
(2) Defining C99 limits in <machine/limits.h> adds pollution to
<limits.h>.

o Implement <sys/_types.h>, a new header for storing types that are
MI, not required to be a fixed size, and used in multiple headers.
This will grow in time, as more things move here from <sys/types.h>
and <machine/ansi.h>.
o Add missing type definitions (uint16_t and uint32_t) to
<arpa/inet.h> and <netinet/in.h>.
o Reduce pollution in <sys/types.h> by using `#if _FOO_T_DECLARED'
widgets to avoid including <sys/stdint.h>.
o Add some missing type definitions to <unistd.h> and note the ones
that still need to be added.
o Make use of <sys/_types.h> primitives in <grp.h> and <sys/types.h>.

Reviewed by: bde

o Add new header <sys/stdint.h>.
o Make <stdint.h> a symbolic link to <sys/stdint.h>.
o Move most of <sys/inttypes.h> into <sys/stdint.h>, as per C99.
o Remove <sys/inttypes.h>.
o Adjust includes in sys/types.h and boot/efi/include/ia64/efibind.h
to reflect new location of integer types in <sys/stdint.h>.
o Remove previously symbolicly linked <inttypes.h>, instead create a
new file.
o Add MD headers <machine/_inttypes.h> from NetBSD.
o Include <sys/stdint.h> in <inttypes.h>, as required by C99; and
include <machine/_inttypes.h> in <inttypes.h>, to fill in the
remaining requirements for <inttypes.h>.
o Add additional integer types in <machine/ansi.h> and
<machine/limits.h> which are included via <sys/stdint.h>.

Partially obtain from: NetBSD
Tested on: alpha, i386
Discussed on: freebsd-standards@bostonradio.org
Reviewed by: bde, fenner, obrien, wollman