Make linux_stop_lwp be a shared function

Both GDB and gdbserver had linux_stop_lwp functions with identical
declarations.  This commit moves these to nat/linux-nat.h to allow
shared code to use the function.

gdb/ChangeLog:

	* linux-nat.h (linux_stop_lwp): Move declaration to...
	* nat/linux-nat.h (linux_stop_lwp): New declaration.

gdb/gdbserver/ChangeLog:

	* linux-low.h (linux_stop_lwp): Remove declaration.

gdb/ChangeLog

@@ -1,3 +1,8 @@
+2015-03-24  Gary Benson  <gbenson@redhat.com>
+
+	* linux-nat.h (linux_stop_lwp): Move declaration to...
+	* nat/linux-nat.h (linux_stop_lwp): New declaration.
+
 2015-03-24  Gary Benson  <gbenson@redhat.com>
 
 	* linux-nat.h: Include nat/linux-nat.h.

gdb/gdbserver/ChangeLog

@@ -1,3 +1,7 @@
+2015-03-24  Gary Benson  <gbenson@redhat.com>
+
+	* linux-low.h (linux_stop_lwp): Remove declaration.
+
 2015-03-24  Gary Benson  <gbenson@redhat.com>
 
 	* linux-low.h: Include nat/linux-nat.h.

gdb/gdbserver/linux-low.h

@@ -355,7 +355,7 @@ int linux_pid_exe_is_elf_64_file (int pid, unsigned int *machine);
 int linux_attach_lwp (ptid_t ptid);
 
 struct lwp_info *find_lwp_pid (ptid_t ptid);
-void linux_stop_lwp (struct lwp_info *lwp);
+/* For linux_stop_lwp see nat/linux-nat.h.  */
 
 #ifdef HAVE_LINUX_REGSETS
 void initialize_regsets_info (struct regsets_info *regsets_info);

gdb/linux-nat.h

@@ -140,7 +140,7 @@ void linux_proc_pending_signals (int pid, sigset_t *pending,
 
 extern int lin_lwp_attach_lwp (ptid_t ptid);
 
-extern void linux_stop_lwp (struct lwp_info *lwp);
+/* For linux_stop_lwp see nat/linux-nat.h.  */
 
 /* Stop all LWPs, synchronously.  (Any events that trigger while LWPs
    are being stopped are left pending.)  */

gdb/nat/linux-nat.h

@@ -47,4 +47,9 @@ extern struct lwp_info *iterate_over_lwps (ptid_t filter,
 					   iterate_over_lwps_ftype callback,
 					   void *data);
 
+/* Cause LWP to stop.  This function must be provided by the
+   client.  */
+
+extern void linux_stop_lwp (struct lwp_info *lwp);
+
 #endif /* LINUX_NAT_H */