Add `_finalizer' to the list of known GNAT auxilary routines.

Add `_finalizer' to the list of known GNAT auxilary routines.

This is a new routine that is being generated by the expander in
the context of controlled types.  This patch adds it to the list of such
routines so that the debugger does not show it when selecting the first
"user" frame (when switching tasks for instance).

gdb/ChangeLog:

        * ada-lang.h (ADA_KNOWN_AUXILIARY_FUNCTION_NAME_PATTERNS): Add
        "_finalizer" to the list.