Add prototype for sigset_from_compat()

Duh.  I screwed up editing David Howells patch in commit
3f2e05e90e0846c42626e3d272454f26be34a1bc, and the actual declaration for
the sigset_from_compat() function went missing. My bad.

Olaf Hering saved the day and noticed that I'm a moron.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>

include/linux/compat.h

@@ -228,6 +228,7 @@ static inline int compat_timespec_compare(struct compat_timespec *lhs,
 asmlinkage long compat_sys_adjtimex(struct compat_timex __user *utp);
 
 extern int compat_printk(const char *fmt, ...);
+extern void sigset_from_compat(sigset_t *set, compat_sigset_t *compat);
 
 #endif /* CONFIG_COMPAT */
 #endif /* _LINUX_COMPAT_H */