PATCH: Use PTRACE_PEEKUSER to get fs_base and gs_base for x32

PTRACE_ARCH_PRCTL is obsolete since 2.6.25, where the fs_base and gs_base
fields of user_regs_struct can be used directly.  Since x32 support was
added to kernel 3.4.0 and PTRACE_ARCH_PRCTL support was removed for x32,
we should always use fs_base/gs_base for x32.  It uses fs_base and gs_base
only if __ILP32__ is defined since they aren't available with the older
header files.  OK to install?

Thanks.

H.J.
---
2012-06-16  Roland McGrath  <roland <at> hack.frob.com>
	    H.J. Lu  <hongjiu.lu <at> intel.com>

	* amd64-linux-nat.c (ps_get_thread_area): Use PTRACE_PEEKUSER
	to get fs_base and gs_base for x32.

diff --git a/gdb/amd64-linux-nat.c b/gdb/amd64-linux-nat.c
index 23eadbd..7a90065 100644
--- a/gdb/amd64-linux-nat.c
+++ b/gdb/amd64-linux-nat.c
 <at>  <at>  -479,12 +479,45  <at>  <at>  ps_get_thread_area (const struct ps_prochandle *ph,
       switch (idx)
 	{
 	case FS:
+#ifdef __ILP32__
+	    {
+	      /* PTRACE_ARCH_PRCTL is obsolete since 2.6.25, where the
+		 fs_base and gs_base fields of user_regs_struct can be
+		 used directly.  Since x32 support was added to kernel