Following some changes on x86-64.

When cpu_has_fxsr is defined to 1 like in many kernels unlazy_fpu can
collapse to three instructions. For that inlining is a very good idea.
Otherwise it's 10 instructions or so, which can be still inlined.

We don't need the lock prefix to test our local thread flags state.
Unfortunately test_thread_flag currently always uses test_bit which
has a LOCK on SMP, but that's unnecessary. LOCK is costly on P4,
so it's a good idea to avoid it.

Work around this for now by testing directly. Better would be
probably to define __set_bit for all architectures to not guarantee
atomicity and then always use that for local thread_info accesses
in linux/thread_info.h