Add support for timeconting in userland.

This diff exposes parts of clock_gettime(2) and gettimeofday(2) to
userland via libc eliberating processes from the need for a context
switch everytime they want to count the passage of time.

If a timecounter clock can be exposed to userland than it needs to set
its tc_user member to a non-zero value. Tested with one or multiple
counters per architecture.

The timing data is shared through a pointer found in the new ELF
auxiliary vector AUX_openbsd_timekeep containing timehands information
that is frequently updated by the kernel.

Timing differences between the last kernel update and the current time
are adjusted in userland by the tc_get_timecount() function inside the
MD usertc.c file.

This permits a much more responsive environment, quite visible in
browsers, office programs and gaming (apparently one is are able to fly
in Minecraft now).

Tested by robert@, sthen@, naddy@, kmos@, phessler@, and many others!

OK from at least kettenis@, cheloha@, naddy@, sthen@

When system calls indicate an error they return -1, not some arbitrary
value < 0. errno is only updated in this case. Change all (most?)
callers of syscalls to follow this better, and let's see if this strictness
helps us in the future.

(struct timezone *)0 -> NULL, while I'm here.

Wrap <time.h> so that internal calls go direct and symbols not in C99 are weak
Add prototypes to localtime.c for offtime(), time2posix(), posix2time() to
reduce noise with -Wmissing-prototypes
Eliminate unnecessary #includes

zap remaining rcsid.

Kill old files that are no longer compiled.

okay theo

KNF + ansification

ok deraadt@, vincent@

Remove the advertising clause in the UCB license which Berkeley
rescinded 22 July 1999. Proofed by myself and Theo.

Fix RCS ids
Make sure everything uses {SYS,}LIBC_SCCS properly

branches: 1.1.1;
Initial revision

When system calls indicate an error they return -1, not some arbitrary
value < 0. errno is only updated in this case. Change all (most?)
callers of syscalls to follow this better, and let's see if this strictness
helps us in the future.

(struct timezone *)0 -> NULL, while I'm here.

Wrap <time.h> so that internal calls go direct and symbols not in C99 are weak
Add prototypes to localtime.c for offtime(), time2posix(), posix2time() to
reduce noise with -Wmissing-prototypes
Eliminate unnecessary #includes

zap remaining rcsid.

Kill old files that are no longer compiled.

okay theo

KNF + ansification

ok deraadt@, vincent@

Remove the advertising clause in the UCB license which Berkeley
rescinded 22 July 1999. Proofed by myself and Theo.

Fix RCS ids
Make sure everything uses {SYS,}LIBC_SCCS properly

branches: 1.1.1;
Initial revision

(struct timezone *)0 -> NULL, while I'm here.

Wrap <time.h> so that internal calls go direct and symbols not in C99 are weak
Add prototypes to localtime.c for offtime(), time2posix(), posix2time() to
reduce noise with -Wmissing-prototypes
Eliminate unnecessary #includes

zap remaining rcsid.

Kill old files that are no longer compiled.

okay theo

KNF + ansification

ok deraadt@, vincent@

Remove the advertising clause in the UCB license which Berkeley
rescinded 22 July 1999. Proofed by myself and Theo.

Fix RCS ids
Make sure everything uses {SYS,}LIBC_SCCS properly

branches: 1.1.1;
Initial revision