Print Ada type name in more cases

In some cases the name of an Ada type cannot be decoded by
decoded_type_name.  For example, the name
"p__complex_variable_record_type__T9s" in the included test case is
rejected due to the "T".  This causes ptype to display the full
contents of a record type -- when in fact the name is available and
ought to be printed.

Fixing this in decoded_type_name isn't possible because the "__T" name
is not the real name of the type -- it is just a compiler-assigned
name of convenience.

This patch fixes the problem by using the resolved type's name when
the original type's name isn't suitable.

gdb/ChangeLog
2020-11-04  Tom Tromey  <tromey@adacore.com>

	* ada-typeprint.c (ada_print_type): Handle __T types.

gdb/testsuite/ChangeLog
2020-11-04  Tom Tromey  <tromey@adacore.com>

	* gdb.ada/rec_ptype.exp: New file.
	* gdb.ada/rec_ptype/main.adb: New file.
	* gdb.ada/rec_ptype/p.ads: New file.