Make "ptype INTERNAL_FUNCTION" in Ada print like other languages

Currently, printing the type of an internal function in Ada shows
double <>s, like:

 (gdb) with language ada -- ptype $_isvoid
 type = <<internal function>>

while all other languages print it with a single <>, like:

 (gdb) with language c -- ptype $_isvoid
 type = <internal function>

I don't think there's a reason that Ada needs to be different.  We
currently print the double <>s because we take this path in
ada_print_type:

    switch (type->code ())
      {
      default:
	gdb_printf (stream, "<");
	c_print_type (type, "", stream, show, level, language_ada, flags);
	gdb_printf (stream, ">");
	break;

... and the type's name already has the <>s.

Fix this by simply adding an early check for
TYPE_CODE_INTERNAL_FUNCTION.

Approved-By: Andrew Burgess <aburgess@redhat.com>
Approved-By: Tom Tromey <tom@tromey.com>
Change-Id: Ic2b6527b9240a367471431023f6e27e6daed5501
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30105