[Python] Make regexp collection printers work with typedefs as well.

Consider the following type for which we would like to provide
a pretty-printer and manage it via RegexpCollectionPrettyPrinter:

        typedef long time_t;

Currently, this does not work because this framework only considers
the type's tag name:

        typename = gdb.types.get_basic_type(val.type).tag
        if not typename:
            return None

This patch extends it to use the type's name if the basic type
does not have a tag name, thus allowing the framework to also
work with typedefs like the above.

gdb/ChangeLog:

        * python/lib/gdb/printing.py (RegexpCollectionPrettyPrinter):
        Use the type's name if its basic type does not have a tag.

gdb/testsuite/ChangeLog:

        * testsuite/gdb.python/py-pp-re-notag.c: New file.
        * testsuite/gdb.python/py-pp-re-notag.ex: New file.
        * testsuite/gdb.python/py-pp-re-notag.p: New file.

gdb/python/lib/gdb/printing.py

@@ -199,6 +199,8 @@ class RegexpCollectionPrettyPrinter(PrettyPrinter):
 
         # Get the type name.
         typename = gdb.types.get_basic_type(val.type).tag
+        if not typename:
+            typename = val.type.name
         if not typename:
             return None