linux-user: define TARGET_ARCH_HAS_KA_RESTORER

Sparc as an extended sigaction structure containing
the field ka_restorer used in place of sa_restorer.

Define TARGET_ARCH_HAS_KA_RESTORER and use it
with sparc.

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20180402102453.9883-2-laurent@vivier.eu>
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 889abbd..b8353d8 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -8699,6 +8699,9 @@
                 target_siginitset(&act.sa_mask, old_act->sa_mask);
                 act.sa_flags = old_act->sa_flags;
                 act.sa_restorer = old_act->sa_restorer;
+#ifdef TARGET_ARCH_HAS_KA_RESTORER
+                act.ka_restorer = 0;
+#endif
                 unlock_user_struct(old_act, arg2, 0);
                 pact = &act;
             } else {
@@ -8773,8 +8776,8 @@
                 if (!lock_user_struct(VERIFY_READ, act, arg2, 1)) {
                     goto efault;
                 }
-#ifdef TARGET_SPARC
-                act->sa_restorer = restorer;
+#ifdef TARGET_ARCH_HAS_KA_RESTORER
+                act->ka_restorer = restorer;
 #endif
             } else {
                 act = NULL;