m68k: define HAVE_SA_RESTORER

On m68k the kernel sigaction structure has the sa_restorer member for
historical reasons.

* signal.c (HAVE_SA_RESTORER): Define for M68K.
diff --git a/signal.c b/signal.c
index 710fb19..867e156 100644
--- a/signal.c
+++ b/signal.c
@@ -62,7 +62,7 @@
 #  define HAVE_SA_RESTORER 1
 # endif
 #else /* !SA_RESTORER */
-# if defined SPARC || defined SPARC64
+# if defined SPARC || defined SPARC64 || defined M68K
 #  define HAVE_SA_RESTORER 1
 # else
 #  define HAVE_SA_RESTORER 0