Enable vgdb ptrace invoker for aarch64.

This only works in non-bi arch mode. If ever aarch64+arm
are compiled bi-arch, then some more work is needed to have
a 64 bits vgdb able to ptrace invoke a 32 bits valgrind.

Note also that PTRACE_GETREGSET is defined on other platforms
(e.g. ppc64 fedora 18 defines it), but it is not used on
these platforms, as again, PTRACE_GETREGSET implies some
work for bi-arch to work properly.
So, on all platforms except arm64, we use PTRACE_GETREGS
or PTRACE_PEEKUSER.



git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13981 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/README.aarch64 b/README.aarch64
index 28a26cc..2d6c936 100644
--- a/README.aarch64
+++ b/README.aarch64
@@ -7,19 +7,17 @@
 instructions and can run anything generated by gcc-4.8.2 -O3.  The
 port is under active development.
 
-Current limitations, as of mid-March 2014.
+Current limitations, as of mid-May 2014.
 
 * limited support of vector (SIMD) instructions.  Initial target is
   support for instructions created by gcc-4.8.2 -O3
   (via autovectorisation).  This is complete.
 
 * Integration with the built in GDB server:
-   - basically works but breakpoints may be problematic (unclear)
-     Use --vgdb=full to bypass the problem.  
+   - works ok (breakpoint, attach to a process blocked in a syscall, ...)
    - still to do:
       arm64 xml register description files (allowing shadow registers
                                             to be looked at).
-      ptrace invoker : currently disabled for both arm and arm64
       cpsr transfer to/from gdb to be looked at (see also arm equivalent code)
 
 * limited syscall support