linux-nat: Add function lwp_is_stepping

Add the function lwp_is_stepping which indicates whether the given LWP
is currently single-stepping.  This is a common interface, usable from
native GDB as well as from gdbserver.

gdb/gdbserver/ChangeLog:

	* linux-low.c (lwp_is_stepping): New function.

gdb/ChangeLog:

	* nat/linux-nat.h (lwp_is_stepping): New declaration.
	* linux-nat.c (lwp_is_stepping): New function.

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2016-09-16  Andreas Arnez  <arnez@linux.vnet.ibm.com>
+
+	* nat/linux-nat.h (lwp_is_stepping): New declaration.
+	* linux-nat.c (lwp_is_stepping): New function.
+
 2016-09-16  Andreas Arnez  <arnez@linux.vnet.ibm.com>
 
 	* s390-linux-nat.c (gdbcmd.h): New include.

gdb/gdbserver/ChangeLog

@@ -1,3 +1,7 @@
+2016-09-16  Andreas Arnez  <arnez@linux.vnet.ibm.com>
+
+	* linux-low.c (lwp_is_stepping): New function.
+
 2016-09-06  Carl Love  <cel@us.ibm.com>
 
 	* server.c (start_inferior):  Fixed comment, requested comment change

gdb/gdbserver/linux-low.c

@@ -176,6 +176,14 @@ lwp_stop_reason (struct lwp_info *lwp)
   return lwp->stop_reason;
 }
 
+/* See nat/linux-nat.h.  */
+
+int
+lwp_is_stepping (struct lwp_info *lwp)
+{
+  return lwp->stepping;
+}
+
 /* A list of all unknown processes which receive stop signals.  Some
    other process will presumably claim each of these as forked
    children momentarily.  */

gdb/linux-nat.c

@@ -355,6 +355,14 @@ lwp_stop_reason (struct lwp_info *lwp)
   return lwp->stop_reason;
 }
 
+/* See nat/linux-nat.h.  */
+
+int
+lwp_is_stepping (struct lwp_info *lwp)
+{
+  return lwp->step;
+}
+
 
 /* Trivial list manipulation functions to keep track of a list of
    new stopped processes.  */

gdb/nat/linux-nat.h

@@ -85,4 +85,9 @@ extern enum target_stop_reason lwp_stop_reason (struct lwp_info *lwp);
 
 extern void linux_stop_lwp (struct lwp_info *lwp);
 
+/* Return nonzero if we are single-stepping this LWP at the ptrace
+   level.  */
+
+extern int lwp_is_stepping (struct lwp_info *lwp);
+
 #endif /* LINUX_NAT_H */