consolidate kernel-side struct sigaction declarations

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/arch/arm/include/asm/signal.h b/arch/arm/include/asm/signal.h
index 5805702..a5076b9 100644
--- a/arch/arm/include/asm/signal.h
+++ b/arch/arm/include/asm/signal.h
@@ -23,12 +23,7 @@
 	__sigrestore_t sa_restorer;
 };
 
-struct sigaction {
-	__sighandler_t sa_handler;
-	unsigned long sa_flags;
-	__sigrestore_t sa_restorer;
-	sigset_t sa_mask;		/* mask last for extensibility */
-};
+#define __ARCH_HAS_SA_RESTORER
 
 #include <asm/sigcontext.h>
 #endif