Refactor the application of type attributes so that attributes from

the declaration-specifiers and on the declarator itself are moved
to the appropriate declarator chunk.  This permits a greatly
simplified model for how to apply these attributes, as well as
allowing a much more efficient query for the GC attribute.
Now all qualifier queries follow the same basic strategy of
"local qualifiers, local qualifiers on the canonical type,
then look through arrays".  This can be easily optimized by
changing the canonical qualified-array-type representation.

Do not process type attributes as decl attributes on declarations
with declarators.

When computing the type of a block, synthesize a prototype
function declarator chunk if the decl-spec type was not a
function.  This simplifies the logic for building block signatures.

Change the logic which inserts an objc_read_weak on a block
literal to only fire if the block has a __weak __block variable,
rather than if the return type of the block is __weak qualified,
which is not actually a sensible thing to ask.

llvm-svn: 122871