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

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

Remove the advertising clause from the UCB license according to the
July 22, 1999 addendum.

netchild's mega-patch to isolate compiler dependencies into a central
place.

This moves the dependency on GCC's and other compiler's features into
the central sys/cdefs.h file, while the individual source files can
then refer to #ifdef __COMPILER_FEATURE_FOO where they by now used to
refer to #if __GNUC__ > 3.1415 && __BARC__ <= 42.

By now, GCC and ICC (the Intel compiler) have been actively tested on
IA32 platforms by netchild. Extension to other compilers is supposed
to be possible, of course.

Submitted by: netchild
Reviewed by: various developers on arch@, some time ago

/* -> /*- for license, minor formatting changes

Standardize idempotentcy ifdefs. Consistently use _MACHINE_VARARGS_H_
symbol.

Add conditionals to allow va_list to be defined in other headers.

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

Gcc 3.1 varargs support.

Standardize idempotentcy ifdefs.

Add kernel headers needed to build libc. Some are bogus and/or just enough
to compile.

Mostly obtained from: netbsd