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/arch/x86/include/asm/signal.h b/arch/x86/include/asm/signal.h
index 598457c..6cbc795 100644
--- a/arch/x86/include/asm/signal.h
+++ b/arch/x86/include/asm/signal.h
@@ -125,6 +125,8 @@
 extern void do_notify_resume(struct pt_regs *, void *, __u32);
 # endif /* __KERNEL__ */
 
+#define __ARCH_HAS_SA_RESTORER
+
 #ifdef __i386__
 # ifdef __KERNEL__
 struct old_sigaction {