Be more agressive about bootstrapping ctfmerge and ctfconvert so
builds from existing releases have a chance of working properly.

Sponsored by:	DARPA, AFRL
MFC after:	3 days
Add a new CPUTYPE supported by Clang 3.3 for AMD Jaguar processors (btver2).
- Document GCC support for AMD Family 10h processors (amdfam10).
- Document Clang support for AMD Jaguar processors (btver2).
Add a missing comma.
Explain remedy for -J error from old make
Minor improvements to <stdatomic.h>.

- Define __SYNC_ATOMICS in case we're using the __sync_*() API. This is
  not used by <stdatomic.h> itself, but may be useful for some of the
  intrinsics code to determine whether it should build the
  machine-dependent intrinsic functions.

- Make is_lock_free() work in kernelspace. For now, assume atomics in
  kernelspace are always lock free. This is a quite reasonable
  assumption, as we surely shouldn't implement the atomic fallbacks for
  arbitrary sizes.
Add C11 atomic fallbacks for ARM.

Basically the situation is as follows:

- When using Clang + armv6, we should not need any intrinsics. It should
  support it, even though due to a target misconfiguration it does not.
  We should fix this in Clang.
- When using Clang + noarmv6, provide __atomic_* functions that disable
  interrupts.
- When using GCC + armv6, we can provide __sync_* intrinsics, similar to
  what we did for MIPS. As ARM and MIPS are quite similar, simply base
  this implementation on the one I did for MIPS.
- When using GCC + noarmv6, disable the interrupts, like we do for
  Clang.

This implementation still lacks functions for noarmv6 userspace. To be
done.
Bring the stdatomic for MIPS code slightly more in sync with the ARM version.