scripts/dump-guest-memory.py: fix int128_get64 on recent gcc

The Int128 is no longer a struct, reaching a python exception:
Python Exception <class 'gdb.error'> Attempt to extract a component of a value that is not a (null).:

Replace struct access with a cast to uint64[] instead.

Fixes:
https://bugzilla.redhat.com/show_bug.cgi?id=1427466Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20170310112819.16760-1-marcandre.lureau@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

scripts/dump-guest-memory.py

@@ -314,8 +314,18 @@ def get_arch_phdr(endianness, elfclass):
 def int128_get64(val):
     """Returns low 64bit part of Int128 struct."""
 
-    assert val["hi"] == 0
-    return val["lo"]
+    try:
+        assert val["hi"] == 0
+        return val["lo"]
+    except gdb.error:
+        u64t = gdb.lookup_type('uint64_t').array(2)
+        u64 = val.cast(u64t)
+        if sys.byteorder == 'little':
+            assert u64[1] == 0
+            return u64[0]
+        else:
+            assert u64[0] == 0
+            return u64[1]
 
 
 def qlist_foreach(head, field_str):