MFC 332891,332892: Fixes for atomic_*cmpset() on arm.

332891:
Fix some harmless type mismatches in the ARM atomic_cmpset implementations.

The return value of atomic_cmpset() and atomic_fcmpset() is an int (which
is really a bool) that has the values 0 or 1. Some of the inlines were
using the type being operated on (e.g. uint32_t) as either the return type
of the function, or the type of a local 'ret' variable used to hold the
return value. Fix all of these to just use plain 'int'. Due to C promotion
rules and the fact that the value can only be 0 or 1, these should all be
harmless.

332892:
Implement 32-bit atomic_fcmpset() in userland for armv4/v5.

• Add an implementation of atomic_fcmpset_32() using RAS for armv4/v5. This fixes recent world breakage due to use of atomic_fcmpset() in userland.
• While here, be more careful to not expose wrapper macros for 64-bit atomic_*cmpset to userland for armv4/v5 as only 32-bit cmpset is implemented.

This has been reviewed, but not runtime-tested, but should fix the arm.arm
and arm.armeb worlds that have been broken for a while.

Approved by: re (kib)