[C] Improve diagnostics for vector types

[Joseph Myers]

On Mon, 30 Sep 2019, Richard Sandiford wrote:

> 2019-09-30  Richard Sandiford  <richard.sandiford@arm.com>
> 
> gcc/c-family/
> 	* c-pretty-print.c (pp_c_specifier_qualifier_list): If a vector type
> 	has a type name, use it in preference to the __vector syntax.
> 
> gcc/testsuite/
> 	* gcc.dg/diag-aka-3.c: New test.
> 	* gcc.target/aarch64/diag_aka_1.c: New test.
> 	* g++.dg/diagnostic/aka4.C: New test.

OK.

-- 
Joseph S. Myers
joseph@codesourcery.com