[PATCH] ppc32: Fix racy access to TI_FLAGS

[PATCH] ppc32: Fix racy access to TI_FLAGS

The ppc32 syscall entry code could access the thread info flags in a
racy way, thus potentially losing bits sets there at interrupt time or
by another CPU, like NEED_RESCHED or SIGPENDING (ouch !).

This fixes it by moving the potentially racy bit to a different field (I
preferred that rather than turning the access into an atomic operation
for performances reasons).