[Bug c/50459] alignof doesn't work on plain old constant, works with expressions containing it

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50459

--- Comment #2 from Marc Glisse <glisse at gcc dot gnu.org> ---
(In reply to Marek Polacek from comment #1)
> The problem on the C side of things is that the values of the enum are
> represented by CONST_DECL nodes and check_user_alignment doesn't look
> through it.  So maybe something like the following?  (Tested x86_64-linux,
> no regressions.)

Note that the problem is not restricted to this attribute, it affects all
attributes taking an integral parameter.