[Sema][Attr]Fix alignment attribute printing.

[Sema][Attr]Fix alignment attribute printing.

Remove "IsMSDeclspec" argument from Align attribute since the arguments in Attr.td should
only model those appear in source code. Introduce attribute Accessor, and teach TableGen
to generate syntax kind accessors for Align attribute, and use those accessors to decide
if an alignment attribute is a declspec attribute.

llvm-svn: 174133