signal: Define __ARCH_HAS_SA_RESTORER so we know whether to clear sa_restorer

Vaguely based on upstream commit 574c4866e33d 'consolidate kernel-side
struct sigaction declarations'.

flush_signal_handlers() needs to know whether sigaction::sa_restorer
is defined, not whether SA_RESTORER is defined.  Define the
__ARCH_HAS_SA_RESTORER macro to indicate this.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/asm-generic/signal.h b/include/asm-generic/signal.h
index 555c0ae..743f7a5 100644
--- a/include/asm-generic/signal.h
+++ b/include/asm-generic/signal.h
@@ -99,6 +99,10 @@
 
 #include <asm-generic/signal-defs.h>
 
+#ifdef SA_RESTORER
+#define __ARCH_HAS_SA_RESTORER
+#endif
+
 struct sigaction {
 	__sighandler_t sa_handler;
 	unsigned long sa_flags;