Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

Copy amd64 stdarg.h to x86 and replace amd64/i386/pc98 stdarg.h with stubs.

Use __builtin_va_start instead of __builtin_stdarg_start. GCC4 obsoletes
the former and __builtin_va_start was present in all GCC version 3.1 and
later.

Remove diffs to i386 version that came in via the compiler support ifdefs.
This changes things like whitespace, inconsistent use of #ifndef vs
#if !defined(), different macro argument orders, mismatched comments, etc.

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

Add __va_copy and make it always visible, in spite of the __ISO_C_VISIBLE
setting. Make va_copy be an alias if __ISO_C_VISIBLE >= 1999.

Why? more than a few ports have an autoconf that looks for __va_copy
because it is available on glibc. It is critical that we use it if
at all possible on amd64. It generally isn't a problem for i386 and its
ilk because autoconf driven code tends to fall back to an assignment.

Provide a fake varargs implementation for lint's benefit. This way
it can see the intent of the va_* macros, even though it cannot work.

Approved by: re (blanket amd64/*)

o Add conditionals to allow va_list to be defined in other headers.
o Standardize on _MACHINE_STDARG_H_ to allow multiple header includes.
o Restrict the definition of va_copy() to C99 environments.

Implement C99's va_copy() macro.

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.