C++ PATCH for c++/17743, 19163 (attribute align in templates)

[Paolo Carlini]

Jason Merrill wrote:
> However, this patch does make aligned_storage work, because uses of 
> aligned_storage involve dependent types, so the type is resolved after 
> we've applied the align attribute.
Independently from the remaining issues, many thanks for this. If I 
understand correctly, will allow to remove all the ugly specializations 
for special values of the alignment from <type_traits>. If nobody beats 
me I'll prepare a patch in a couple of days...

Paolo.