Re: gdb 10.1: wrong argument lookup code is used for x86_64 frame

For my purposes, I could fix this by adding a 
amd64_fetch_pointer_argumentfunction to amd64-tdep.c:

```

static CORE_ADDR
amd64_fetch_pointer_argument (struct frame_info *frame, int argi,
               struct type *type)
{
   struct gdbarch *gdbarch = get_frame_arch (frame);
   enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
   CORE_ADDR sp;
   int regnum;
   int len;

   switch( argi)
   {
   case 0  : regnum = AMD64_RDI_REGNUM; break;
   case 1  : regnum = AMD64_RSI_REGNUM; break;
   case 2  : regnum = AMD64_RDX_REGNUM; break;
   case 3  : regnum = AMD64_RCX_REGNUM; break;
   case 4  : regnum = AMD64_R8_REGNUM; break;
   case 5  : regnum = AMD64_R9_REGNUM; break;

   default : sp  = get_frame_register_unsigned( frame, AMD64_RSP_REGNUM);
             len = gdbarch_ptr_bit( gdbarch) / 8;
             return read_memory_unsigned_integer (sp + (len * (argi - 
5)), len, byte_order);
   }
   return( get_frame_register_unsigned( frame, regnum));
}

```

The `default:` code path is probably trash :)


And I put this into `amd64_init_abi`:

```

set_gdbarch_fetch_pointer_argument (gdbarch, amd64_fetch_pointer_argument);
```


Ciao

   Nat!