Move "used FPU status" into new non-atomic thread_info->status field.

Move "used FPU status" into new non-atomic thread_info->status field.

This allows us to avoid having to use atomic updates for the lazy FP
status setting, since we don't have to worry about other CPU's racing
on the fields.

Also, fix x86 FP state after fork() by making sure the FP is unlazied
_before_ we copy the state information. Otherwise, if a process did a
fork() while holding the FP state lazily in the registers, the child
would incorrectly unlazy bogus state.