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

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

Use aux vector to get values for SSP canary, pagesize, pagesizes array,
number of host CPUs and osreldate.

This eliminates the last sysctl(2) calls from the dynamically linked image
startup.

No objections from: kan
Tested by: marius (sparc64)
MFC after: 1 month

Add prototype for libc internal interfaces.

Change the C wrappers for mmap/lseek/pread/pwrite/truncate/ftruncate to
call the pad-less versions of the corresponding syscalls if the running
kernel supports it. Check kern.osreldate once per program and cache the
result to select the appropriate syscall. This maintains userland
compatability with kernel.old's from quite a while back.

Approved by: re (kensmith)