arch/tile: Change struct sigcontext to be more useful

Rather than just using pt_regs, it now contains the actual saved
state explicitly, similar to pt_regs.  By doing it this way, we
provide a cleaner API for userspace (or equivalently, we avoid the
need for libc to provide its own definition of sigcontext).

While we're at it, move PT_FLAGS_xxx to where they are not visible
from userspace.  And always pass siginfo and mcontext to signal
handlers, even if they claim they don't need it, since sometimes
they actually try to use it anyway in practice.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>

arch/tile/include/asm/signal.h

@@ -24,6 +24,7 @@
 #include <asm-generic/signal.h>
 
 #if defined(__KERNEL__) && !defined(__ASSEMBLY__)
+struct pt_regs;
 int restore_sigcontext(struct pt_regs *, struct sigcontext __user *, long *);
 int setup_sigcontext(struct sigcontext __user *, struct pt_regs *);
 void do_signal(struct pt_regs *regs);