libstdc++: Fix std::any pretty printer [PR 68735]

This fixes errors seen on powerpc64 (big endian only) due to the
printers for std::any and std::experimental::any being unable to find
the manager function.

libstdc++-v3/ChangeLog:

	PR libstdc++/65480
	PR libstdc++/68735
	* python/libstdcxx/v6/printers.py (function_pointer_to_name):
	New helper function to get the name of a function from its
	address.
	(StdExpAnyPrinter.__init__): Use it.

libstdc++-v3/python/libstdcxx/v6/printers.py

@@ -1126,6 +1126,29 @@ class SingleObjContainerPrinter(object):
             return self.visualizer.display_hint ()
         return self.hint
 
+def function_pointer_to_name(f):
+    "Find the name of the function referred to by the gdb.Value f, "
+    " which should contain a function pointer from the program."
+
+    # Turn the function pointer into an actual address.
+    # This is needed to unpack ppc64 function descriptors.
+    f = f.dereference().address
+
+    if sys.version_info[0] == 2:
+        # Older versions of GDB need to use long for Python 2,
+        # because int(f) on 64-bit big-endian values raises a
+        # gdb.error saying "Cannot convert value to int."
+        f = long(f)
+    else:
+        f = int(f)
+
+    try:
+        # If the function can't be found older versions of GDB raise a
+        # RuntimeError saying "Cannot locate object file for block."
+        return gdb.block_for_pc(f).function.name
+    except:
+        return None
+
 class StdExpAnyPrinter(SingleObjContainerPrinter):
     "Print a std::any or std::experimental::any"
 
@@ -1138,11 +1161,11 @@ class StdExpAnyPrinter(SingleObjContainerPrinter):
         visualizer = None
         mgr = self.val['_M_manager']
         if mgr != 0:
-            func = gdb.block_for_pc(int(mgr.cast(gdb.lookup_type('intptr_t'))))
+            func = function_pointer_to_name(mgr)
             if not func:
-                raise ValueError("Invalid function pointer in %s" % self.typename)
+                raise ValueError("Invalid function pointer in %s" % (self.typename))
             rx = r"""({0}::_Manager_\w+<.*>)::_S_manage\((enum )?{0}::_Op, (const {0}|{0} const) ?\*, (union )?{0}::_Arg ?\*\)""".format(typename)
-            m = re.match(rx, func.function.name)
+            m = re.match(rx, func)
             if not m:
                 raise ValueError("Unknown manager function in %s" % self.typename)