Properly compute the alignment of typedefs that make use of the

"aligned" attribute. Previously, we were skipping over these
attributes when we jumped directly to the canonical type. Now,
ASTContext::getTypeInfo walks through typedefs and other
"non-canonical" types manually, looking for "aligned" attributes on
typedefs.

As part of this change, I moved the GNU-specific logic (such as
determining the alignment of void or of a function pointer) out of the
expression evaluator and into ASTContext::getTypeInfo.

llvm-svn: 70497